单选题Cell membranes act as barriers to most, but not all, molecules. Development of a cell membrane that could allow some materials to pass while constraining the movement of other molecules was a major step in the evolution of the cell. Cell membranes are differentially permeable barriers separating the inner cellular environment from the outer cellular (or external) environment. Water potential is the tendency of water to move from an area of higher concentration to one of lower concentration. Energy exists in two forms: potential and kinetic. Water molecules move according to differences in potential energy between where they are and where they are going. Gravity and pressure are two enabling forces for this movement. These forces also operate in the hydrologic (water) cycle. Remember in the hydrologic cycle that water runs downhill (likewise it falls from the sky, to get into the sky it must be acted on by the sun and evaporated, thus needing energy input to power the cycle). Diffusion is the net movement of a substance (liquid or gas) from an area of higher concentration to one of lower concentration. You are on a large (10ftx10ftx10ft) elevator. An obnoxious individual with a lit cigar gets on at the third floor with the cigar still burning. You are also unfortunate enough to be in a very tall building and the person says "Hey we're both going to the 62nd floor!" Disliking smoke you move to the farthest corner you can. Eventually you are unable to escape the smoke! An example of diffusion in action. Nearer the source the concentration of a given substance increases. You probably experience this in class when someone arrives freshly doused in perfume or cologne, especially the cheap stuff. Since the molecules of any substance (solid, liquid, or gas) are in motion when that substance is above absolute zero (0 degrees Kelvin or -273 degrees C), energy is available for movement of the molecules from a higher potential state to a lower potential state, just as in the case of the water discussed above. The majority of the molecules move from higher to lower concentration, although there will be some that move from low to high. The overall (or net) movement is thus from high to low concentration. Eventually, if no energy is input into the system the molecules will reach a state of equilibrium where they will be distributed equally throughout the system. The cell membrane functions as a semi-permeable barrier, allowing a very few molecules across it while fencing the majority of organically produced chemicals inside the cell. Electron microscopic examinations of cell membranes have led to the development of the lipid bilayer model (also referred to as the fluid-mosaic model). The most common molecule in the model is the phospholipid, which has a polar (hydrophilic) head and two nonpolar (hydrophobic) tails. These phospholipids are aligned tail to tail so the nonpolar areas form a hydrophobic region between the hydrophilic heads on the inner and outer surfaces of the membrane. This layering is termed a bilayer since an electron microscopic technique known as freeze-fracturing is able to split the bilayer.

单选题In a seeming contradiction, the growth of computer-augmented work will probably create a need for less-skilled workers rather than the reverse. While early computers required much knowledge and skill to operate, comprehensive software packages have virtually eliminated the requirement for technical knowledge. Indeed, advanced software may lead to a decreased need for certain job-related skills. For example , word processing has reduced the need for secretarial typing accuracy, since mistakes can be corrected quickly and easily with no trace of correction. Spell-checking programs can be relied on to prevent common mistakes, thus decreasing the need for that language skill. We have already encountered cashiers who have no need to compute a customer' s change. Instead, they merely enter the purchase amount and then the amount offered in payment. The machine calculates the change and, in some cases, automatically dispenses it. This effect is seen in more complex jobs, too. Nurses in intensive-care units often monitor several patients from a central station. Digital readouts continuously report patients' vital signs. A-larms sound if values exceed an expected range. Despite the obvious advantages computerization has brought to both patient and staff, some health-care professionals are concerned that they may be losing important " soft" skills. The most important of these may be the intuition born of experience acquired in personally observing hundreds or thousands of patients. The look in a patient' s eyes, the coloring of skin and the appearance of pain or restlessness are among many indicators used by medical personnel to anticipate changes in patient condition. These cannot be captured on a digital display. It cannot be denied that computers have made great contributions to productivity, nor would any reasonable person encourage scrapping the technology. However, we must pay more attention to human needs, and to the long-range effects of making jobs less interesting and decreasing skill requirements.

单选题Recent studies of the human brain have resulted in some interesting discoveries. Scientists believe that a way to improve the power of the brain may soon be possible. Scientists have discovered that the brain can make its own drugs. The brain【C1】______a protein substance which can act directly【C2】______the brain to change aspects of mental activity. Some may change or improve, for example, creativity, intelligence, imagination, and good【C3】______. Chemicals found in the brain【C4】______messages. In recent years scientists have found chemicals that【C5】______mood, memory and other happenings of the mind. About 25 have been found【C6】______. Today the role of chemicals and the protein substance in human behavior is creating much interest. Research seems to show that they may help【C7】______insomnia, pain, and mental illness. They have a great【C8】______to stimulate the brain to【C9】______deficiencies. They also improve the qualities of memory and learning already in the brain. They【C10】______the secret on mood and emotion. Some day there may be a chemical way to create a better and more efficient brain.

单选题Auctions are public sales of goods, conducted by an officially approved auctioneer. He asked the crowd to gather in the auction room to bid for various items on sale. He encourages buyers to bid higher figures and finally names the highest bidder as the buyer of the goods. This is called "knocking down" the goods, for the bidding ends when the auctioneer bangs a small hammer on a raised platform. The ancient Romans probably invented sales by auction and the English word comes from the Latin "autic", meaning "increase". The Romans usually sold in this way the spoils taken in war; these sales were called "sub hasta", meaning "under the spear", a spear being stuck in the ground as a signal for a crowd to gather. In England in the eighteenth and nineteenth centuries goods were often sold "by the candle"; a short candle was lit by the auctioneer and bids could be made while it was burning. Practically all goods can be sold by auction. Among these are coffee, skins, wool, tea, cocoa, furs, fruit, vegetables and wines. Auction sales are also usual for land and property, antique furniture, pictures, rare books, old china and works of art. The auction rooms at Chritie's and Sotheby's in London and New York are world famous. An auction is usually advertised beforehand with full particulars of the articles to be sold and where and when they can be viewed by the buyers. If the advertisement cannot give full details, catalogues are printed, and each group of goods to be sold together, called a "lot", is usually given a number. The auctioneer need not begin with lot one and continue the numerical order; he may wait until he notices the fact that certain buyers are in the room and then produce the lots they are likely to be interested in. The auctioneer's services are paid for in the form of a percentage of the price the goods are sold for. The auctioneer therefore has a direct interest in pushing up the bidding.

单选题The bird flu virus is mutating and becoming more dangerous to mammals, according to researchers. The discovery reinforces fears that a human pandemic of the disease could yet occur. Avian flu hit the headlines in 1997 when a strain called H5N1 jumped from chickens to people, killing 6 people in Hong Kong. Within 3 days, the country's entire chicken population was slaughtered and the outbreak was controlled. Since then new strains of virus have emerged, killing a further 14 people. As yet, no strain has been able to jump routinely from person to person. But if a more virulent strain evolves, the fear is that it could trigger widespread outbreaks, potentially affecting millions of people. Now, genetic and animal studies show that the virus is becoming more menacing to mammals. Immediate action is needed to stem the virus's transmission, says Hualan Chen from Harbin Veterinary Research Institute, China, who was involved in the research. Chen and colleagues studied 21 H5N1 flu virus samples taken from apparently healthy ducks, which act as a natural reservoir for the disease, in southern China between 1999 and 2002. The researchers inoculated groups of chickens, mice and ducks with virus samples taken from different years and waited to see which animals became ill. Their results are presented this week in the Proceedings of the National Academy of Sciences. As expected, ducks were immune to the virus's effects and the chickens fell sick. However, the mice also became ill, losing weight and the use of their limbs. Crucially, the severity of their illness was linked with the year from which the virus sample was taken. Viruses isolated in 2001 and 2002 made the animals more ill than those isolated earlier on. The findings hint that some time around 2001, the virus became adept at infecting mammals. Genetic analysis of the same samples reveals that the virus's DNA changed over that time, suggesting that accumulated mutations may have contributed to the increased virulence. Researchers are concerned that a virus that has acquired the ability to infect mice could also infect humans. "The disease could resurge at any time, " warns virologist Marion Koopmans from the National Institute of Public Health and the Environment in Bilthoven, the Netherlands. The findings highlight the need for improved surveillance to ensure that any future outbreaks are curtailed, she says. Although domestic poultry are easily culled, wild animals are more difficult to contain. "It is impossible to eradicate the natural reservoir, " says Koopmans, "so we need to learn to live with it. " Birds may not be the only villains in this story, however. Chen believes that pigs may also play a part. In Asia, chickens and pigs are often kept in close proximity, so the virus may have shuffled back and forth between the 2 species, picking up mutations and becoming better at infecting mammalian hosts. Humans may then have caught the disease from swine.

单选题Everyone has seen it happen. A colleague who has been excited, involved, and productive slowly begins to pull back, lose energy and interest, and becomes a shadow or his or her former self. Or, a person who has been a beacon of vision and idealism retreats into despair or cynicism. What happened? How does someone who is capable and committed become a person who functions minimally and does not seem to care for the job or the people that work there? Burnout is a chronic state of depleted energy, lack of commitment and involvement, and continual frustration, often accompanied at work by physical symptoms, disability claims and performance problem. Job burnout is a crisis of spirit, when work that was once exciting and meaningful becomes deadening. An organization" s most valuable resource—the energy, dedication, and creativity of its employees—is often squandered by a climate that limits or frustrates the pool of talent and energy available. Milder forms of burnout are a problem at every level in every type of work. The burned-out manager comes to work, but he brings a shell rather than a person. He experiences little satisfaction, and feels uninvolved, detached, and uncommitted to his work and co-workers. While he may be effective by external standards, he works far below his own level of productivity. The people a-round him are deeply affected by his attitude and energy level, and the whole community begins to suffer. Burnout is a crisis of the spirit because people who burn out were once on fire. It" s especially scary and consequential because it strikes some of the most talented. If they can" t maintain their fire, others ask who can? Are these people lost forever, or can the inner flame be rekindled? People often feel that burnout just comes upon them and that they are helpless victims of it. Actually, the evidence is growing that there were ways for individuals to safeguard and renew their spirit, and more important, there are ways for organizations to change conditions that lead to burnout.

单选题Famed singer Steve Wonder can" t see his fans dancing at his concerts. He can" t see the hands of his audience as they applaud wildly at the end of his Superstition. Blind from birth, Wonder has waited his whole life for a chance to see. Recently, Wonder visited Mark Humayan, a vision specialist. He thought that a new device currently being studied by Humayan might offer him that chance. The device, a retinal prosthesis, is a tiny computer chip implanted inside a patient" s eye. The chip sends images to the brain and allows some sightless people to see shapes and colors. Wonder hoped the retinal prosthesis might work for him. "I" ve always said that if ever there" s possibility of my seeing," said Wonder, "then I would take the challenge. " Unfortunately for Wonder, that challenge will have to wait. Humayan explained that the device isn" t ready for people who have been blind since birth. Their brains may not be able to handle signals from a retinal prosthesis because their brains have never handled signals from a healthy eye. However the retinal prosthesis and other devices show great promise in helping many other sightless people who once had vision see again. Perhaps one day soon, some formerly sightless people may be in Wonder" s audience looking up—and seeing him—for the very first time. Wonder" s willingness to take part in retinal prosthesis studies and the results of those studies are giving new hope to people who thought they would be blind for the rest of their lives. More than one million people in the United States are considered legally blind, meaning that their eyesight is severely impaired. Another one million are totally blind. Two types of specialized cells in the retina—rods and cones—are critical for proper vision. Light enters the eye and fails on the rods and cones in the retina. Those cells convert the light to electrical signals, which travel through the optic nerve to the brain. The brain interprets those signals as visual images. Rods detect light at low levels of illumination. For instance, rods allow you to see faint shadows in dim moonlight. Cones, on the other hand, are most sensitive to color. Some diseases can damage cells in the retina. For instance, macular degeneration causes blindness and other vision problems in 700,000 people in the United States each year. The condition is caused by a lack of adequate blood supply to the central part of the retina. Without blood, the rods, cones, and other cells in the retina die. Devices such as the retinal prosthesis won" t prevent or cure our eye diseases, but they may help patients who have eye disorders regain some of their vision. Different forms of retinal prosthesis are currently being developed. On one type, a tiny computer chip is embedded in the eye. The chip has a grid of about 2,500 light-sensing elements called pixels. Light entering the eye strikes the pixels, which convert the light into electrical signals. The pixels then send the electrical signals to nerve cells behind the retina. Those cells send signals via the optic nerve to the brain for interpretation. Many people who have had a retinal prosthesis implanted say they can see shapes, colors, and movements that they couldn" t see before. "It was great," said Harold Churchey, who received his retinal prosthesis 15 years after he became totally blind. "To see light after so long—it was just wonderful. It was just like switching a light on. "

单选题Imagine eating everything delicious you want—with none of the fat. That would be great, wouldn't it? New "fake fat" products appeared on store shelves in the United States recently, but not everyone is happy about it. Makers of the products, which contain a compound called olestra, say food manufacturers can now eliminate fat from certain foods. Critics, however, say the new compound can rob the body of essential vitamins and nutrients (营养物) and can also cause unpleasant side effects in some people. So it's up to decide whether the new fat-free products taste good enough to keep eating. Chemists discovered olestra in the late 1960s, when they were searching for a fat that could be digested by infants more easily. Instead of finding the desired fat, the researchers created a fat that can't be digested at all. Normally, special chemicals in the intestines (肠) "grab" molecules of regular fat and break them down so they can be used by the body. A molecule of regular fat is made up of three molecules of substances called fatty acids. The fatty acids are absorbed by the intestines and bring with them the essential vitamins A, D, E, and K. When fat molecules are present in the intestines with any of those vitamins, the vitamins attach to the molecules and are carried into the bloodstream. Olestra, which is made from six to eight molecules of fatty acids, is too large for the intestines to absorb. It just slides through the intestines without being broken down. Manufacturers say it' s that ability to slide unchanged through the intestines that make olestra as valuable as a fat substitute. It provides consumers with the taste of regular fat without any bad effects on the body. But critics say olestra can prevent vitamins A, D, E, and K from being absorbed. It can also prevent the absorption of carotenoids (类胡萝卜素 ), compounds that may reduce the risk of cancer, heart disease, etc.. Manufacturers are adding vitamins A, D, E, and K as well as carotenoids to their products now. Even so some nutritionists are still concerned that people might eat unlimited amounts of food made with the fat substitute without worrying about how many calories they are consuming.

单选题What draws my firm's attention is the design of cities. When we designed America' s first "green" office building two decades ago, we felt very【C1】______ . But today, the idea that buildings can be good for people and the environment will be increasingly influential in years to come. Back in 1984 we discovered that most manufactured products for decoration weren' t designed for【C2】______ uses. The "energy-efficient" buildings constructed after the 1970s energy crisis revealed indoor air quality problems caused by materials such as paints and carpet. So, we've been focusing on these materials【C3】______ to the molecules, looking for ways to make them safe for people and the planet. Home builders can now use materials that don't【C4】______ the quality of the air, water, or soil.【C5】______ our basic design strategy is focused not simply on being "less bad" ,but on creating completely healthful materials that can be either safely returned to the soil【C6】______ reused by industry again. In fact, the world' s largest manufacturer has already【C7】______ a fully and safely recyclable carpet. No one【C8】______ to create a building that destroys the planet. But our current industrial systems are inevitably causing these conditions. So【C9】______ simply trying to reduce the damage, we are adopting a positive approach. We' re giving people healthful products and an opportunity to make choices that have a【C10】______ effect on the world. It's not just the building industry. Entire cities are taking these environmentally positive approaches to desian. olannina and buildina.

单选题In the villages of the English countryside there are still people who remember the good old days when no one bothered to lock their doors. There simply wasn"t any crime to worry about. Amazingly, these happy times appear still to be with us in the world"s biggest community. A new study by Dan Farmer, a gifted programmer, using an automated investigative program of his own called SATAN, shows that the owners of well over half of all World Wide Web sites have set up homes without fitting locks to their doors. SATAN can try out a variety of well-known hacking tricks on an Internet site without actually breaking in. Farmer has made the program publicly available, amid much criticism. A person with evil intent could use it to hunt down sites that are easy to burgle. But Farmer is very concerned about the need to alert the public to poor security and, so far, events have proved him right. SATAN has done more to alert people to the risks than cause new disorder. So is the Net becoming more secure? Far from it. In the early days, when you visited a Web site your browser simply looked at the content. Now the Web is full of tiny programs that automatically download when you look at a Web page, and run on your own machine. These programs could, if their authors wished, do all kinds of nasty things to your computer. At the same time, the Net is increasingly populated with spiders, worms, agents and other types of automated beasts designed to penetrate the sites and seek out and classify information. All these make wonderful tools for antisocial people who want to invade weak sites and cause damage. But let"s look on the bright side. Given the lack of locks, the Internet is surely the world"s biggest(almost)crime-free society. Maybe that is because hackers are fundamentally honest. Or that there currently isn"t much to steal. Or because vandalism isn"t much fun unless you have a peculiar dislike for someone. Whatever the reason, let"s enjoy it while we can. But expect it all to change, and security to become the number one issue, when the most influential inhabitants of the Net are selling services they want to be paid for.

单选题Patients whose eyes have suffered heat or chemical burns typically experience severe damage to the cornea—the thin, transparent front of the eye that refracts light and contributes most of the eye's focusing ability. In a long-term study, Italian researchers use stem cells taken from the limbus, the border between the cornea and the white of the eye, to cultivate a graft of healthy cells in a lab to help restore vision in eyes. During the 10-years study, the researchers implanted the healthy stem cells into the damaged cornea in 113 eyes of 112 patients. The treatment was fully successful in more than 75 percent of the patients, and partially successful in 13 percent. Moreover, the restored vision remained stable over 10 years. Success was defined as an absence of all symptoms and permanent restoration of the cornea. Treatment outcome was initially assessed at one year, with up to 10 years of follow-up evaluations. The procedure was even successful in several patients whose burn injuries had occurred years earlier and who had already undergone surgery. Current treatment for burned eyes involves taking stem cells from a patient's healthy eye, or from the eyes of another person, and transferring them to the burned eye. The new procedure, however, stimulates the limbal stem cells from the patient's own eye to reproduce in a lab culture. Several types of treatments using stem cells have proven successful in restoring vision, but the long-term effectiveness shown here is significant. The treatment is only for blindness caused by damage to the cornea; it is not effective for repairing damaged retinas or optic nerves. Chemical eye burns often occur in the workplace, but can also happen due to mishaps involving household cleaning products and automobile batteries. The results of the study, based at Italy's University of Modena and Reggio Emilia, were published in the June 23 online issue of the New England Journal of Medicine.

单选题A number of personal characteristics play a vital role in the development of one"s intelligence. But people fail to realize the significance of cultivating these factors in young people. The "non-intelligence factors" include one"s feelings, will, motivation, interests and habits, etc. After a 30-year follow-up study of 8000 males, American psychologists【C1】______that the main cause of disparities in intelligence is not intelligence itself, but non-intelligence factors including the desire to learn, will-power and self-confidence. 【C2】______people all know that one should have definite objectives, a strong will and good learning habits, quite a number of teachers and parents don"t pay much attention to cultivating these factors. Some parents are greatly worried【C3】______their children fail to do well in their studies. They blame either genetic factors, malnutrition, or laziness, but they never take into consideration these non-intelligence factors. At the same time, some teachers don"t inquire into the reason why students do poorly. They simply give them more course and exercises, or【C4】______rebuke or ridicule them. After all, these students lose self-confidence. Some of them just feel defeated and【C5】______themselves up as hopeless. Others may go astray because they are sick of learning. An investigation of more than 1,000 middle students in Shanghai showed that 46.5 percent of them were【C6】______of learning, because of examination, 36.4 percent lacked persistence, initiative and conscientiousness and 10.3 percent were sick of learning. It is clear that the lack of cultivation of non-intelligence factors has been a main【C7】______to intelligence development in teenagers. It even causes an imbalance between physiological and【C8】______development among a few students. If we don"t start now to strengthen the cultivation of non-intelligence factors, it will not only obstruct the development of the【C9】______of teenagers, but also affect the quality of a whole generation. Some experts have put forward proposals about how to cultivate student"s non-intelligence factors. First, parents and teachers should【C10】______understand teenage psychology. On this basic, they can help them to pursue the objectives of learning, stimulating their interests and toughening their willpower.

单选题Long-suffering couples take heart. There is a good reason for those endless arguments in the front of the car: men and women use different parts of the brain when they try to find their way a-round, suggesting that the strategies they use might also be completely different. Matthias Riepe and his colleagues at the University of Ulm in Germany asked 24 healthy volunteers—half of them men, half women—to find their way out of three virtual-reality mazes displayed on video goggles. Meanwhile, the researchers monitored the volunteers" brain activity using a functional magnetic resonance imaging(fMRI)scanner. This showed that men and women called on strikingly different brain areas to complete the task. "I didn" t expect it to be so dramatic," says Riepe. Previous studies have been shown that women rely mainly on landmarks to find their way. Men use these cues too, but they also use geometric cues, such as the angle and shape of a wall or a corner. Such studies also suggest that men navigate their way out of unfamiliar spaces more quickly, as Riepe found in his study, too. Riepe discovered that both men and women used parts of the parietal cortex towards the top of the brain, the right side of the hippocampus and a few other well-established areas to find their way out. Neuroscientists think that the parietal regions help translate what the eyes see into information about where the body is in space, while the hippocampal region helps process how objects are arranged. But other regions seemed to be exclusively male or female. The men engaged the left side of their hippocampus, which the researchers say could help with assessing geometry or remembering whether they have already visited a location. The women, by contrast, recruited their right frontal cortex. Riepe says this may indicate that they were using their "working memory" , trying to keep in mind the landmarks they had passed. "It fits very well with the animal studies," says Riepe. He points out that there seem to be similar differences in rats. For example, damage to the frontal lobe will impair a female" s sense of direction, but not a male" s.

单选题The 18th-century statesman, Edmund Burke, once said "All that is needed for the triumph of a misguided cause is that good people do nothing." One such cause now seeks to end biomedical research because of the theory that animals have rights ruling out their use in research. Scientists need to respond forcefully to animal rights advocates, whose arguments are confusing the public and thereby threatening advances in health knowledge and care. Leaders of the animal rights movement target biomedical research because it depends on public funding, and few people understand the process of health care research. Hearing description of cruelty to animals in research settings, many are puzzled that anyone would deliberately harm an animal in medical researchers. For example, a grandmotherly woman advocating animal rights at a recent street fair was distributing a brochure that encouraged readers not to use anything that comes from or is tested in animals—no meat, no fur, no medicines. Asked if she opposed immunizations (免疫注射), she wanted to know if vaccines (疫苗) come from animal research. When assured that they do, she replied, "Then I would have to say yes. "Asked what will happen when epidemics return, she said, "Don't worry, scientists will find some way of using computers." Such well-meaning people just don't understand. Scientist must communicate their message to the public in a sympathetic, understandable way—in human terms, not in the language of molecular biology. We need to make clear the connection between animal research and a grandmother's hip replacement, a father's bypass operation, a baby's vaccinations, and even a pet' s shots. To those who are unaware that animal research was needed to produce these treatments, as well as new treatments and vaccines, animal research seems wasteful at best and cruel at worst. Much can be done. Scientists could adopt middle school classes and present their own research. They should be quick to respond to letters to the editor, lest animal rights misinformation go unchallenged and acquire a deceptive appearance of truth. Research institutions could be opened to tours, to show that laboratory animals receive humane care. Finally, because the ultimate stakeholders are patients, the health research community should actively recruit to its cause not only well-known personalities such as Stephen Cooper, who has made courageous statements about the value of animal research, but all who receive medical treatment. If good people do nothing, there is a real possibility that an uninformed citizenry will extinguish the precious embers (余火) of medical progress.

单选题A simple test that detects nicotine levels in urine has helped pregnant women in Birmingham to cut down on cigarettes and in some cases to kick the habit altogether. The test turns urine pink in the presence of nicotine and its breakdown products. " It is very important that the patient is right there to see it," says Graham Cope, a research fellow at the Wolfson Applied Technology Laboratory at the University of Birmingham , who developed the test. A recent survey by the baby's charity Tommy' s Campaign found that a quarter of pregnant women in Britain smoke throughout their pregnancy. But most of the information doctors get about their patients' smoking habits is self-reported. "Smokers tend to underestimate their consumption," says Cope. Even if a smoker owns up (供认) , it is hard to know how much nicotine they are actually consuming; different brands of cigarette have different nicotine levels, and styles of inhaling vary. Cope's device provides the first quick biochemical measure of tobacco absorption. Thiobarbituric acid and other chemicals react with nicotine and its by-products, such as cotinine, to produce the pink color. The more tobacco the smoker has consumed, the pinker it gets. Researchers then use a standard colorimeter to measure the depth of color in order to quantify consumption. In all, the procedure takes five minutes. Cope is just completing a pilot (试验性的) study in which he has screened 1 000 pregnant women in Birmingham. Half of them were tested and shown the results on their first visit. They were screened at least once more, towards the end of their pregnancy. The others were screened but were not given the results. Of the 500 women who were shown their results, just over 100 were smokers. During their pregnancy, 20 percent of them quit, while another 30 percent significantly reduced the amount they smoked. Even among the 50 percent of smokers who said they had not changed their habits, the test showed that about half had in fact cut down. "They were more aware of their habit," says Cope. In contrast, only about 7 percent of the women in the control group managed to quit. Very few cut down, and 45 percent actually increased the amount they smoked. This compares badly to the results in the test group, where only 15 percent smoked more.

单选题Federal Reserve System, central banking system of the United States, popularly called the Fed. A central bank serves as the banker to both the banking community and the government; it also issues the national currency, conducts monetary policy, and plays a major role in supervision and regulation of banks and bank holding companies. In the U.S. these functions are the responsibilities of key officials of the Federal Reserve System: the Board of Governors located in Washington, D. C, and the top officers of the 12 district Federal Reserve banks, located throughout the nation. The Fed"s actions, described below, generally have a significant effect on the U.S. interest rates and, subsequently, on stock, bond, and other financial markets. The Federal Reserve"s basic powers are concentrated in the Board of Governors, which is paramount in all policy issues concerning bank regulation and supervision and in most aspects of monetary control. The board enunciates the Fed"s policies on both monetary and banking matters. Because the board is not an operating agency, most of the day-to-day implementation of policies decisions is left to the district Federal Reserve banks, stock in which is owned by the commercial banks that are members of the Federal Reserve System. Ownership in this instance, however, does not imply control; the Board of Governors and the heads of the Reserve banks orient their policies to the public interest rather than to the benefit of the private banking system. The U.S. banking system"s regulatory apparatus is complex; the authority of the Federal Reserve is shared in some instances for example, in mergers or the examination of banks with other federal agencies such as the Comptroller of the Currency and the Federal Deposit Insurance Cooperation(FDIC). In the critical area of regulating the nation"s money supply in accordance with national economic goals, however, the Federal Reserve is independent within the government. Income and expenditures of the Federal Reserve banks and of the Board of Governors are not subject to the congressional appropriation process; the Federal Reserve is subject to the congressional appropriation process; the Federal Reserve is self-financing. Its income($20.2 billion in 1992)comes mainly from Reserve bank holdings of income-earning securities, primarily those of the U.S. government. Outlays($1.5 billion in 1992)are mostly for operational expenses in providing services to the government and for expenditures connected with regulation and monetary policy. In 1992 the Federal Reserve returned $16.8 billion in earnings to the U.S. Treasury.

单选题For a Nobel laureate, the molecular biologist Max Perutz made a lot of mistakes. His science was strewn with assertions that were not supported by the sparse evidence he had gathered. No matter. He was eventually right about the important things—and gentleman enough to concede his errors. With bloody-minded persistence, Perutz mastered the painstaking task of analyzing images of haemoglobin, the component of blood that carries oxygen. This was no mean feat: a molecule of haemogiobin consists of thousands of atoms and, at the time, only simple structures of tens of atoms had been mapped. It was for this work that Perutz was awarded the Nobel Prize in chemistry in 1962. But his triumphal announcement of the correct structure of haemoglobin was by no means his first solution to the problem: he had previously claimed all sorts of unlikely arrangements, backing down each time a colleague spotted a fatal flaw. Even when he did finally hold the secret to why blood supports life, he did not piece together the evidence to produce the ultimate result. Indeed, Perutz was furious when a junior researcher saw how the final piece fitted and could not resist popping it into its slot, completing what Perutz viewed as his jigsaw puzzle. Nevertheless, it was Perutz who had gathered all the pieces and who ensured, in the end, that they were correctly assembled. Perutz was long the outsider. Of Jewish descent, he was a lapsed Catholic by religion. He left his native Austria in 1936, two years before Hitler annexed it. The outbreak of war saw him expelled to Canada as an enemy alien. On returning to Cambridge, he was not welcomed by his college. It was only after he won the Nobel prize that he felt accepted as an Englishman, despite having been naturalised as a British subject 20 years earlier. As a scientist, too, Perutz was always on the fringe. His field of endeavour, X-ray crystallography, was neither physics nor maths nor chemistry nor biology but a combination of these. As often happens to researchers working in interdisciplinary areas of science, his progress was impeded by an establishment that sought to promote exiting subjects. He lived from grant to grant, each lasting a matter of months. Nevertheless, he managed to establish the unit in which James Watson and Francis Crick elucidated the double helix structure of DNA. A decade later, a whole institute was established under him. Georgina Ferry's biography captures not only the scientific advances made by Perutz but also his curious personal qualities. A skinny, sickly and for much of his life, skint individual, Perutz is an unlikely hero. He was demanding—his diet required him to eat black bananas, even in February—and he was unself-conscious in ensuring that his elaborate needs were met. He was also naive in insisting that scientific reasoning would trump political thought and religious treating. Ms. Ferry portrays his foibles sympathetically. Perutz used to complain that, although he was famous, few people knew what it was he had achieved. By combining scientific with personal anecdotes, her book goes a good way towards redressing that balance.

单选题Less than a year ago, a new generation of diet pills seemed to offer the long sought answer to our chronic weight problems. Hundreds of thousands of pound-conscious Americans had discovered that a drug combination known as "fen-phen" could shut off voracious (贪吃的) appetites like magic, and the FDA had just approved a new drug, Redux, that did the same with fewer side effects. Redux would attract hundreds of thousands of new pill poppers within a few months. But now the diet-drug revolution is facing a backlash. Some of the nation's largest HMOs, including Aetna U. S. Healthcare and Prudential Healthcare have begun cutting back or eliminating reimbursement (退款补偿，报销) for both pills. Diet chains like Jenny Craig and Nutri/System are backing away from them too. Several states, meanwhile, have restricted the use of fen-phen. Last week the Florida legislature banned new prescriptions entirely and called on doctors to wean (使断绝) current patients from the drug within 30 days. It also put a 90-day limit on Redux prescriptions. Even New Jersey doctor Sheldon Levine, who touted Redux last year on TV and in his book The Redux Revolution, has stopped giving it to all but his most obese (肥胖的) patients. The reason for all the retrenchment (紧缩，删节): potentially lethal side effects. Over the summer, the FDA revealed that 82 patients had developed defects in their heart values while on fen-phen, and that seven patients had come down with the same condition on Redux. As if that weren't bad enough, physicians reported that a woman who had been taking fen-phen for less than a month died of primary pulmonary hypertension, a sometimes fatal lung condition already associated with Redux. And an article in the Journal of the American Medical Association last month confirmed earlier reports that both fen-phen and Redux can cause brain damage in lab animals. These findings led the New England Journal to publish editorial admonishing doctors to prescribe the drugs only for patients with severe obesity. Meanwhile, FDA asked drug makers to put more explicit warnings on fen-phen and Redux labels. Since mid-July, prescriptions for fen-phen have dropped 56%, and those for Redux 36%, according to IMS America, a pharmaceutical market research firm. All that really does, however, is to bring the numbers down to where they should have been all along. Manufacturers said from the start that their pills offered a short-term therapy for the obese, not for people looking to fit into a smaller bathing suit. FDA approved Redux with just such a caveat, and when limited to these patients, the drugs may still make sense—despite the risks—because morbid obesity carries its own dangers, including heart disease, diabetes and stroke. Too often, however, Redux and fen-phen were peddled to all comers, almost like candy. The current backlash, says Levine, is a "roller coaster that never should have happened".

单选题Today we make room for a remarkably narrow range of personality styles. We're told that to be great is to be bold, to be happy is to be sociable. We see ourselves as a nation of extroverts — which means that we've lost sight of who we really are. One-third to one-half of Americans are introverts — in the other words, one out of every two or three people you know. If you're not an introvert yourself, you are surely raising, managing, married to, or coupled with one. If these statistics surprise you, that's probably because so many people pretend to be extroverts. Closet introverts pass undetected on playgrounds, in high school locker rooms, and in the corridors of corporate America. Some fool even themselves, until some life event — a layoff, an empty nest, an inheritance that frees them to spend time as they like — jolts them into taking stock of their true natures. You have only to raise this subject with your friends and acquaintances to find that the most unlikely people consider themselves introverts. It makes sense that so many introverts hide even from themselves. We live with a value system that I call the Extrovert Ideal — the omnipresent belief that the ideal self is gregarious, alpha, and comfortable in the spotlight. The archetypal extrovert prefers action to contemplation, risk-taking to heed-taking, certainty to doubt. He favors quick decisions, even at the risk of being wrong. She works well in teams and socializes in groups. We like to think that we value individuality, but all too often we admire one type of individual — the kind who's comfortable "putting himself out there. " Sure, we allow technologically gifted loners who launch companies in garages to have any personality they please, but they are the exceptions, not the rule, and our tolerance extends mainly to those who get fabulously wealthy or hold the promise of doing so. Introversion — along with its cousins' sensitivity, seriousness, and shyness — is now a second-class personality trait, somewhere between a disappointment and a pathology. Introverts living under the Extrovert Ideal are like women in a man's world, discounted because of a trait that goes to the core of who they are. Extroversion is an enormously appealing personality style, but we've turned it into an oppressive standard to which most of us feel we must conform. The Extrovert Ideal has been documented in many studies, though this research has never been grouped under a single name. Talkative people, for example, are rated as smarter, better-looking, more interesting, and more desirable as friends. Velocity of speech counts as well as volume: we rank fast talkers as more competent and likable than slow ones. Even the word introvert is stigmatized — one informal study, by psychologist Laurie Helgoe, found that introverts described their own physical appearance in vivid language, but when asked to describe generic introverts they drew a bland and distasteful picture. But we make a grave mistake to embrace the Extrovert Ideal so unthinkingly. Some of our greatest ideas, art, and inventions — from the theory of evolution to van Gogh's sunflowers to the personal computer — came from quiet and cerebral people who knew how to tune in to their inner worlds and the treasures to be found there.

单选题British scientists are preparing to launch trials of a radical new way to fight cancer, which kills tumours by infecting them with viruses like the common cold. If successful, virus therapy could eventually form a third pillar alongside radiotherapy and chemotherapy in the standard arsenal against cancer, while avoiding some of the debilitating side-effects. Leonard Seymour, a professor of gene therapy at Oxford University, who has been working on the virus therapy with colleagues in London and the US, will lead the trials later this year. Cancer Research UK said yesterday that it was excited by the potential of Prof. Seymour's pioneering techniques. One of the country's leading geneticists, Prof. Seymour has been working with viruses that kill cancer cells directly, while avoiding harm to healthy tissue. "In principle, you've got something which could be many times more effective than regular chemotherapy, " he said. Cancer-killing viruses exploit the fact that cancer cells suppress the body's local immune system. "If a cancer doesn't do that, the immune system wipes it out. If you can get a virus into a tumour, viruses find them a very good place to be because there's no immune system to stop them replicating. You can regard it as the cancer's Achilles' heel. " Only a small amount of the virus needs to get to the cancer. "They replicate, you get a million copies in each cell and the cell bursts and they infect the tumour cells adjacent and repeat the process, " said Prof. Seymour. Preliminary research on mice shows that the viruses work well on tumours resistant to standard cancer drugs. "It's an interesting possibility that they may have an advantage in killing drug-resistant tumours, which could be quite different to anything we've had before. " Researchers have known for some time that viruses can kill tumour cells and some aspects of the work have already been published in scientific journals. American scientists have previously injected viruses directly into tumours but this technique will not work if the cancer is inaccessible or has spread throughout the body. Prof. Seymour's innovative solution is to mask the virus from the body's immune system, effectively allowing the viruses to do what chemotherapy drugs do—spread through the blood and reach tumours wherever they are. The big hurdle has always been to find a way to deliver viruses to tumours via the bloodstream without the body's immune system destroying them on the way. "What we've done is make chemical modifications to the virus to put a polymer coat around it - it's a stealth virus when you inject it, " he said. After the stealth virus infects the tumour, it replicates, but the copies do not have the chemical modifications. If they escape from the tumour, the copies will be quickly recognised and mopped up by the body's immune system. The therapy would be especially useful for secondary cancers, called metastases, which sometimes spread around the body after the first tumour appears. "There's an awful statistic of patients in the west. . . with malignant cancers; 75% of them go on to die from metastases, " said Prof. Seymour. Two viruses are likely to be examined in the first clinical trials: adenovirus, which normally causes a cold-like illness, and vaccinia, which causes cowpox and is also used in the vaccine against smallpox. For safety reasons, both will be disabled to make them less pathogenic in the trial, but Prof. Seymour said he eventually hopes to use natural viruses. The first trials will use uncoated adenovirus and vaccinia and will be delivered locally to liver tumours, in order to establish whether the treatment is safe in humans and what dose of virus will be needed. Several more years of trials will be needed, eventually also on the polymer-coated viruses, before the therapy can be considered for use in the NHS. Though the approach will be examined at first for cancers that do not respond to conventional treatments, Prof. Seymour hopes that one day it might be applied to all cancers.