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 is 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Americans believe no one stands still. If you are not moving ahead, you are falling behind. This attitude results in a nation of people committed to researching, experimenting and exploring. Time is the element that Americans save carefully. "We are slaves to nothing but the clock", it has been said. Time is treated as if it were something almost tangible, it is a precious commodity. Many people have a rather acute sense of the shortness of each lifetime. Once the sands have run out of a person's hourglass, they cannot be replaced. We want every minute to count. A foreigner's first impression of the U. S. is likely to be that everyone is in a rush—often under pressure. City people appear always to be hurrying to get where they are going, elbowing others as they try to complete their errands. Racing through daytime meals is part of the pace of life in this country. People in public eating-places are waiting for you to finish so they can be served and get back to work within the time allowed. Many newcomers to the States will miss the opening courtesies of a business call, for example. They will miss the ritual socializing that goes with a welcoming cup of tea or coffee that may be traditional in their own country. Normally, Americans do not assess their visitors in such relaxed surroundings over prolonged small talk; much less do they take them out for dinner, or around on the golf course while they develop a sense of trust and rapport. Rapport to most of us is less important than performance. We seek out evidence of past performances rather than evaluate a business colleague through social courtesies. Since we generally assess and probe professionally rather than socially, we start talking business very quickly. Some new arrivals will come from cultures where it is considered impolite to work too quickly. Unless a certain amount of time is allowed to elapse, it seems in their eyes as if the task being considered were insignificant, not worthy of proper respect. Assignments are thus felt to be added weight by the passage of time. In the U. S., however, it is taken as a sign of competence to solve a problem, or fulfill a job successfully, with rapidity. Usually, the more important a task is, the more capital, energy, and attention will be poured into it in order to "get it moving".

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It is said that in England death is pressing, in Canada inevitable and in California optional. Small wonder. Americans" life expectancy has nearly doubled over the past century. Failing hips can be replaced, clinical depression controlled, cataracts removed in a 30-minute surgical procedure. Such advances offer the aging population a quality of life that was unimaginable when I entered medicine 50 years ago. But not even a great health-care system can cure death—and our failure to confront that reality now threatens this greatness of ours. Death is normal; we are genetically programmed to disintegrate and perish, even under ideal conditions. We all understand that at some level, yet as medical consumers we treat death as a problem to be solved. Shielded by third-party payers from the cost of our care, we demand everything that can possibly be done for us, even if it" s useless. The most obvious example is late-stage cancer care. Physicians frustrated by their inability to cure the disease and fearing loss of hope in the patient—too often offer aggressive treatment far beyond what is scientifically justified. In 1950, the U. S. spent 0.7 billion on health care. In 2002, the cost will be billion. Anyone can see this trend is unsustainable. Yet few seem willing to try to reverse it. Some scholars conclude that a government with finite resources should simply stop paying for medical care that sustains life beyond a certain age—say 83 or so. Former Colorado governor Richard Lamm has been quoted as saying that the old and infirm "have a duty to die and get out of the way" , so that younger, heallhier people can realize their potential. I would not go that far. Energetic people now routinely work through their 60s and beyond, and remain dazzlingly productive. At 78, Viacom chairman Sumner Redstone- jokingly claims to be 53. Supreme Court Justice Sandra Day O" Connor is in her 70s, and former surgeon general C. Everett Koop chairs an Internet start-up in his 80s. These leaders are living proof that prevention works and that we can manage the health problems that come naturally with age. As a mere 68-year-old, I wish to age as productively as they have. Yet there are limits to what a society can spend in this pursuit. As a physician, I know the most costly and dramatic measures may be ineffective and painful. I also know that people in Japan and Sweden, countries that spend far less on medical care, have achieved longer, healthier lives than we have. As a nation, we may be overfunding the quest for unlikely cures while underfunding research on humbler therapies that could improve people" s lives.

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.

单选题"In every known human society the male's needs for achievement can be recognized. . . In a great number of human societies men's sureness of their sex role is tied up with their right, or ability, to practice some activity that women are not allowed to practice. Their maleness in fact has to be underwritten by preventing women from entering some field or performing some feat. " This is the conclusion of the anthropologist Margaret Mead about the way in which the roles of men and women in society should be distinguished. If talk and print are considered it would seem that the formal emancipation of women is far from complete. There is a flow of publications about the continuing domestic bondage of women and about the complicated system of defences which men have thrown up around their hitherto accepted advantages, taking sometimes the obvious form of exclusion from types of occupation and sociable groupings, and sometimes the more subtle form of automatic doubt of the seriousness of women's pretensions to the level of intellect and resolution that men, it is supposed, bring to the business of running the world. There are a good many objective pieces of evidence for the erosion of men's status. In the first place, there is the widespread postwar phenomenon of the woman Prime Minister, in India, Sri Lanka and Israel. Secondly, there is the very large increase in the number of women who work, especially married women and mothers of children. More diffusely there are the increasingly numerous convergences between male and female behaviour: the approximation to identical styles in dress and coiffure, the sharing of domestic tasks, and the admission of women to all sorts of hitherto exclusively male leisure-time activities. Everyone carries round with him a fairly definite idea of the primitive or natural conditions of human life. It is acquired more by the study of humorous cartoons than of archaelology, but that does not matter since it is not significant as theory but only as an expression of inwardly felt expectations of people's sense of what is fundamentally proper in the differentiation between the roles of the two sexes. In this rudimentary natural society men go out to hunt and fish and to fight off the tribe next door while women keep the fire going. Amorous initiative is firmly reserved to the man, who sets about courtship with a club.

单选题Although genetic mutations in bacteria and viruses can lead to epidemics, some epidemics are caused by bacteria and viruses that have undergone no significant genetic change. In analyzing the latter, scientists have discovered the importance of social and ecological factors to epidemics. Poliomyelitis, for example, emerged as an epidemic in the United States in the twentieth century, by then, modern sanitation was able to delay exposure to polio until adolescence or adulthood, at which time polio infection produced paralysis. Previously, infection had occurred during infancy, when it typically provided lifelong immunity without paralysis. Thus, the hygiene that helped prevent typhoid epidemics indirectly fostered a paralytic polio epidemic. Another example is Lyme disease, which is caused by bacteria that are transmitted by deer ticks. It occurred only sporadically during the late nineteenth century, but has recently become prevalent in parts of the United States, largely due to an increase in the deer population that occurred simultaneously with the growth of the suburbs and increased outdoor recreational activities in the deer's habitat. Similarly, an outbreak of dengue hemorrhagic fever became an epidemic in Asia in the 1950s because of ecological changes that caused Aedesaegypti, the mosquito that transmits the dengue virus, to proliferate. The stage is now set in the United States for a dengue epidemic because of the inadvertent introduction and wide dissemination of another mosquito, Aedesalbopictus.

单选题When it comes to health, which is more important, nature or nurture? You may well think your genes are a more important predictor of health and ill health. Not so fast. In fact, it transpires that our everyday environment outweighs our genetics, big time, when it comes to measuring our risk of disease. The genome is out—welcome the exposome. "The exposome represents everything a person is exposed to in the environment, that's not in the genes, " says Stephen Rappaport, environmental health scientist at the University of California, Berkeley. That includes stress, diet, lifestyle choices, recreational and medicinal drug use and infections, to name a few. "The big difference is that the exposome changes throughout life as our bodies, diets and lifestyles change, " he says. While our understanding of the human genome has been growing at an exponential rate over the last decade, it is not as helpful as we hoped in predicting diseases. "Genes only contribute 10 percent to the overall disease burden, " says Rappaport. "Knowing genetic risk factors can prove absolutely futile , " says Jeremy Nicholson at Imperial College London. He points to work by Nina Paynter at the Brigham and Women's Hospital in Boston, who investigated the effect of 101 genetic markers implicated in heart disease. After following over 19, 000 women for 12 years, she found these markers were not able to predict anything about the incidence of heart disease in this group. On the other hand, the impact of environmental influences is still largely a mystery. " There's an imbalance between our ability to investigate the genome and the environment, " says Chris Wild, director of the International Agency for Research on Cancer, who came up with the idea of the exposome. In reality, most diseases are probably caused by a combination of the two, which is where the exposome comes in. "The idea is to have a comprehensive analysis of a person's full exposure history, " says Wild. He hopes a better understanding of exposures will shed a brighter light on disease risk factors. There are likely to be critical periods of exposure in development. For example, the time from birth to 3 years of age is thought to be particularly important. "We know that this is the time when brain connections are made, and that if you are obese by this age, you'll have problems as an adult, " says Nicholson.

单选题Among the most stressful of worries are death, illness, loss of work, money problem, marital problems and retirement. Such worries have rational basis, but we are curiously irrational in the way we pursue them. For example, fear of death is as strong among young adults as among the elderly. It is equally surprising that we are as worried the hour before having a tooth filled as when we face major surgery. It is difficult to decide at what point worrying ceases to be "normal", but it is clearly reasonable to worry. People get seriously ill, planes go awry, tube trains sometimes crash. In practice, anxiety is judged to be pathological when it curtails our ability to lead a normal existence. We can manage perfectly well without travelling in planes or lifts, and an evening out isn" t spoiled by the fact that we are unable to leave the house without triple-checking the frontdoor lock. Such worries are widespread in the general population. In its extreme form, anxiety may be experienced either as a generalized, "free-floating" state(the sufferer becomes tense and frightened for no apparent reason), or it may be more specifically focused - for example on open spaces, enclosed situations or certain insects or animals. Many people will have experienced the former - taut muscles, dry mouth and the feeling of agitation, dread or even panic - while mild phobias are also very common. But at less intense levels, anxiety and worrying have great value. They help us to avoid trouble, or to cope with it when it cannot be avoided. Worrying may be an internal impulse, allowing us to solve problems at times of crisis. By worrying, we may understand better the origins of the worry and thereby avoid a possible breakdown. It may also play a significant part in helping us to come to terms with reality. In everyday life, anxiety energizes us and improves performance of a wide variety of tasks, it also galvanizes us to achieve more. Without it, it is difficult to see how there could be either social or intellectual progress. So worrying is not after all an unproductive activity. Perhaps the time to be worried is when you" re not worrying.