单选题People have worded about smog for many years, and the government has spent billions of dollars to try to clean up the air of big cities. Now we find that there is no escape from unhealthful air. Recent studies have shown that air inside many homes, office buildings, and schools is full of pollutants: chemicals, bacteria, smoke, and gases. These pollutants are causing a group of unpleasant and dangerous symptoms that experts call "sick building syndrome". A "sick building" might be a small house in a rural area or an enormous office building in an urban center. A recent study reached a surprising conclusion: Indoor air pollution is almost always two to five times worse than outside pollution! This is true even in buildings that are close to factories that produce chemicals. The solution to this problem would seem very clear: Open your windows and stay out of modern office buildings with windows that don't open. Unfortunately, the solution might not be so simple, better ventilation—a system for moving fresh air—can cut indoor air pollution to a safe level, but lack of ventilation is seldom the main cause of the problem. Experts have found that buildings create their own pollution. Imagine a typical home. The people who live there burn oil, wood, or gas for cooking and heating. They might smoke cigarettes, pipes, or cigars. They use chemicals for cleaning. They use hundreds of products made of plastic or particle board; these products—such as the shelves in Oakland High School—give off chemicals that we can't see but that we do breathe in. And in many areas, the ground under the building might send a dangerous gas called radon into the home. The people in the house are breathing in a "chemical soup", and medical experts don't yet know how dangerous this is for the human body.

单选题The elements other than hydrogen and helium exist in such small quantities that it is accurate to say that the universe is somewhat more than 75 percent hydrogen. Astronomers have measured the abundance of helium throughout our galaxy and in other galaxies as well. Helium has been found in old stars, in relatively young ones, in interstellar gas, and in the distant objects known as quasars. Helium nuclei have also been found to be constituents of cosmic rays that fall on the earth(cosmic "rays" are not really a form of radiation; they consist of rapidly moving particles of numerous different kinds). It doesn"t seem to make very much difference where the helium is found. Its relative abundance never seems to vary much. In some places, there may be slightly more of it; in others, slightly less, but the ratio of helium to hydrogen nuclei always remains about the same. Helium is created in stars. In fact, nuclear reactions that convert hydrogen to helium are responsible for most of the energy that stars produce. However, the amount of helium that could have been produced in this manner can be calculated, and it turns out to be no more than a few percent. The universe has not existed long enough for this figure to be significantly greater. Consequently, if the universe is somewhat more than 25 percent helium now, then it must have been about 25 percent helium at a time near the beginning. However, when the universe was less than one minute old, no helium could have existed. Calculations indicate that before this time temperatures were too high and particles of matter were moving around much too rapidly. It was only after the one-minute point that helium could exist. By this time, the universe had cooled sufficiently that neutrons and protons could stick together. But the nuclear reactions that led to the formation of helium went on for only a relatively short time. By the time the universe was a few minutes old, helium production had effectively ceased.

单选题A little information is a dangerous thing. A lot of information, if it's inaccurate or confusing even more so. This is a problem for anyone trying to spend or invest in an environmentally sustainable way. Investors are barraged with indexes purporting to describe companies eco-credentials, some of dubious quality Green labels on consumer products are ubiquitous, but their claims are hard to verify. The confusion is evident from the New Scientists' analysis of whether public perception of companies' green credentials reflect reality. It shows that many companies considered "green" have done little to earn that reputation, while others do not get sufficient credit for their efforts to reduce their environmental impact. Obtaining better information is crucial, because decisions by consumers and big investors will help propel us towards a green economy. At present, it is too easy to make unverified claims. Take disclosure of greenhouse gas emission, for example. There are voluntary schemes such as a Carbon Disclosure Project, but little scrutiny of the figures companies submit, which means investors may be misled. Measurements can be difficult to interpret, too, like those for water use. In this case, context is crucial: a little from rain-soaked Ireland is not the same as a little drawn from the Arizona desert. Similar problems bedevil "green" labels attached to individual products. Here, the computer equipment rating system developed by the Green Electronics Council shows the way forward. Its criteria come from the IEEE, the world's leading, professional association for technology. Other schemes, such as the "sustainability index" planned by US retail giant Walmart, are broader. Devising rigorous standard for a large number of different types of products will be tough, placing a huge burden on the academic-led consortium that is doing the underlying scientific work. Our investigation also reveals that many companies choose not to disclose data. Some will want to keep it that way. This is why we need legal requirements for full disclosure of environmental information, with the clear message that the polluter will eventually be required to pay. The market forces will drive companies to lean up their acts. Let's hope we can rise to this challenge. Before we can have a green economy we need a green information economy—and it's the quality of information, as well as the quality, that will count.

单选题People who live and work in areas with elevated levels of ozone and other airborne pollutants appear to run an increased risk of lung cancer, US researchers report in the December Issue of the Journal Environmental Health Perspectives. The researchers, Dr. Beeson, of Texas University and colleagues studied more than 4,000 female and 2,000 male, white, nonsmoking volunteers from 1977 to 1992. At the start of the study, the volunteers filled out questionnaires about their occupations, their exercise patterns, diet and other lifestyle choices, and their family" s health history. The questionnaires also asked whether the volunteers had any respiratory symptoms, how many hours they spent outdoors, and where they lived and worked. The researchers updated this information in 1987 and again in 1992. Using air quality monitoring station data, Beeson and colleagues then determined the levels of particle soot, ozone or "smog", sulfur dioxide, and other pollutants that the volunteers were exposed to, given where they lived and worked. Over the course of the 15-year study, 20 of the women and 16 of the men were diagnosed with lung cancer. Analyzing the relationship between exposure to airborne pollutants and lung cancer risk, the researchers found that both men and women regularly exposed to levels of particle that were higher than the National Ambient Air Quality Standard of 50 microgram per meter cubed ran an increased risk of lung cancer. And both men and women exposed to elevated levels of sulfur dioxide ran an increased risk of lung cancer. In addition, men regularly exposed to ozone levels of 80 parts per billion(ppb)ran more than three times the risk of lung cancer as men exposed to lower levels. The Environmental Protection Agency(EPA)limit on ozone is 120 ppb, Beeson and colleagues report. Women, however, did not appear to run an increased risk of lung cancer if exposed to high levels of smog. " This gender difference may be due to the males spending much more time outdoors than females," they write. "This was especially true for the summer when ozone levels are higher. " The difference may also have been due to hormonal differences, they add. Some research findings also suggest that the female sex hormone estrogen may partly offset the consequences of exposure to high ozone levels. "Our findings suggest that the current EPA standard of 120 ppb for ozone may not adequately protect the large portion of the US male population who live or work in communities where the current standard for ozone is frequently exceeded," Beeson and colleagues conclude. "More research with a larger number of incident cases of lung cancer is needed to better understand the observed gender difference in regard to ozone exposure as well as to better separate the independent effects of ozone, airborne particulate matter sulfur dioxide, and other airborne pollutants. "

单选题When people are struck by lightning, they fall to the ground as though they were struck by a severe blow to the head. After the shock they may remain unconscious, become semiconscious or be conscious but confused and dazed, at least for a time. Flashes of light may continue passing before their eyes, and blindness and deafness may follow. The nervous system may be badly affected, causing paralysis, pain in the limbs and even hemorrhage. There will be burns where the lightening passed through the body, and like all electrical bunts, they are often deep and severe. All persons, especially campers and hunters, should know how to give first aid to someone who has been struck by lightning. Do not be afraid to touch the victim. You won't get a shock. The lightening has already been grounded. Remember that speed is of the greatest importance in severe cases. The first thing to do is to loosen tight clothing about the throat and waist. Then clear the air passages of mucus (粘液) if present, and apply artificial respiration if necessary. Give mouth-to-mouth resuscitatiorn if needed, or give oxygen if available. Many victims thought to be dead have been revived after treatment. Send someone for a doctor as soon as possible, but don't leave the victim alone. If a doctor is not available, take the person to a hospital as soon as the person can be safely moved. Signs of shock are: pale, cold, sticky skin; weak, rapid pulse, shallow, irregular breathing or, in extreme cases, no breathing at all. To treat shock, you must keep the patient lying down with the head lower than the feet and cover him or her with a blanket but watch out for overheating. Giving a stimulating hot tea or coffee will help, but only if the patient is thoroughly conscious. After breathing has been restored and shock is treated, treat the burns. Apply some salve and cover them with a clean cloth or a sterile dressing. If conscious, the patient will be badly frightened, so do all you can to reassure. A little knowledge and a helping hand may save someone' s life.

单选题When imaginative men turn their eyes towards space and wonder whether life exists in any part of it, they may cheer themselves by remembering that life need not resemble closely the life that exists on Earth. Mars looks like the only planet where life like ours could exist, and even this is doubtful. But there may be other kinds of life based on other kinds of chemistry and they may multiply on Venus or Jupiter. At least we cannot prove at present that they do not. Even more interesting is the possibility that life on their planets may be in a more advanced stage of evolution. Present-day man is in a peculiar and probably temporary stage. His individual units retain a strong sense of personality. They are, in fact, still capable under favorable circumstances of leading individual lives. But man's societies are already sufficiently developed to have enormously more power and effectiveness than the individuals have. It is not likely that this transitional situation will continue very long on the evolutionary time scale. Fifty thousand years from now man's societies may have become so close-knit that the individuals retain no sense of separate personality. Then little distinction will remain between the organic parts of the multiple organism and the inorganic parts (machines) that have been constructed by it. A million years further on man and his machines may have merged as closely as the muscles of the human body and the nerve cells that set them in motion. The explorers of space should be prepared for some such situation. If they arrive on a foreign planet that has reached an advanced stage (and this is by no means impossible), they may find it being inhabited by a single large organism composed of many closely cooperating units. The units may be "secondary" — machines created millions of years ago by a previous form of life and given the will and ability to survive and reproduce. They may be built entirely of metals and other durable materials, if this is the case, they may be much more tolerant of their environment multiplying under conditions that would destroy immediately any organism made of carbon compound and dependent on the familiar carbon cycle. Such creatures might be relics of a past age, many millions of years ago, when their planet was favorable to the origin of life or they might be immigrants from a favored planet.

单选题There are only three available strategies for controlling cancer: prevention, screening and treatment. Lung cancer causes more deaths than any other types of cancer. A major cause of the disease is not【C1】______known; there is no good evidence that screening is much help; and treatment fails in about 90 percent of all cases. At present, therefore, the main strategy must be【C2】______. This may not always be true, of course, as for some other types of cancer, researches over the past few decades have produced(or suggested)some importance in prevention, screening or treatment. 【C3】______. however, we consider not what researchers may one day offer but what today"s knowledge could already deliver that is not being delivered, then the most practical and cost-efficient opportunities for avoiding premature death from cancer, especially lung cancer, probably involve neither screening nor improved【C4】______. but prevention. This conclusion does not depend on the unrealistic assumption that we can eliminate tobacco. It merely assumes that we can reduce cigarette sales appreciably by raising prices or by【C5】______on the type of education that already appears to have a positive effect on cigarette assumption by white-collar workers and that we can substantially reduce the amount of tar【C6】______per cigarette. The practicability of preventing cancer by such measures applies not only in those countries, such as, the United States of America, because cigarette smoking has been common for decades, 25 to 30 percent of all cancer deaths now involves lung cancer, but also in those where it has become【C7】______only recently. In China, lung cancer as yet accounts for only 5 to 10 percent of all cancer deaths. This is because it may take as much as half a century for the rise in smoking to increase in the incidence to lung cancer. Countries where cigarette smoking is only now becoming widespread can expect enormous increase in lung cancer during the 1990"s or early in the next century,【C8】______prompt effective action is taken against the habit— indeed, such increase are already plainly evident in parts of the world. There are reasons why the preventions of lung cancer is of such overwhelming importance. First, the disease is extremely common, causing more deaths than any other types of cancer now【C9】______; secondly, it is generally incurable; thirdly, effective, practicable measures to reduce its incidence are already reliably known; and finally, reducing tobacco consumption will also have a substantial【C10】______on many other diseases.

单选题You can have too much of a good thing, it seems—at least when it comes to physiotherapy after a stroke. Many doctors believe that it is the key to recovery; exercising a partially paralyzed limb can help the brain "rewire" itself and replace neural connections destroyed by a clot in the brain. But the latest animal experiments suggest that too much exercise too soon after a brain injury can make the damage worse. "It" s something that clinicians are not aware of," says Timothy Schallert of the University at Austin, who led the research. In some trials, stroke victims asked to put their good arm in a sling—to force them to use their partially paralyzed limb—had made much better recoveries than those who used their good arm. But these patients were treated many months after their strokes. Earlier intervention, Schallert reasoned, should lead to even more dramatic improvements. To test this theory, Schallert and his colleagues placed tiny casts on the good forelimbs of rats for two weeks immediately after they were given a small brain injury that partially paralyzed one forelimb. Several weeks later, the researchers were astonished to find that brain tissue surrounding the original injury had also died. "The size of the injury doubled. It" s a very dramatic effect. " says Schallert. Brain-injured rats that were not forced to overuse their partially paralyzed limbs showed no similar damage, and the casts did not cause a dramatic loss of brain tissue in animals that had not already suffered minor brain damage. In subsequent experiments, the researchers have found that the critical period for exercise-induced damage in rats is the first week after the initial brain injury. The spreading brain damage witnessed by Schaller" s team was probably caused by the release of glutamate, a neurotransmitter, from brain cells stimulated during limb movement. At high doses, glutamate is toxic even to healthy nerve cells. And Schallert believes that a brain injury makes neighboring cells unusually susceptible to the neurotransmitter" s toxic effects. Randolph Nudo of the University of Texas Health Science Center at Houston, who studies brain injury in primates, agrees that glutamate is the most likely culprit. In experiments with squirrel monkeys suffering from stroke-like damage, Nudo tried beginning rehabilitation within five days of injury. Although the treatment was beneficial in the long run, Nudo noticed an initial worsening of the paralysis that might also have been due to brain damage brought on by exercise.Schallert stresses that mild exercise is likely to be beneficial however soon it begins. He adds that it is unclear whether human victims of strokes, like brain-injured rats, could make their problems worse by exercising too vigorously, too soon. Some clinics do encourage patients to begin physiotherapy within a few weeks of suffering a traumatic head injury or stroke, says David Hovda, director of brain injury research at the University of California, Los Angeles. But even if humans do have a similar period of vulnerability to rat, he speculates that it might be possible to use drugs to block the effects of glutamate.

单选题This week some top scientists, including Nobel Prize winners, gave their vision of how the world will look in 2056, from gas-powered cars to extraordinary health advances, John Ingham reports on what the world"s finest minds believe our futures will be. For those of us lucky enough to live that long, 2056 will be a world of almost perpetual youth, where obesity is a remote memory and robots become our companions. We will be rubbing shoulders with aliens and colonizing outer space. Better still, our descendants might at last live in a world at peace with itself. Will we really, as today"s scientists claim, be able to live for ever or at least cheat the ageing process so that the average person lives to 150? Of course, all these predictions come with a scientific health warning. Harvard professor Steven Pinker says: "This is an invitation to look foolish, as with the predictions of domed cities and nuclear-powered vacuum cleaners that were made 50 years ago." Living longer Anthony Atala, director of the Wake Forest Institute in North Carolina, believes failing organs will be repaired by injecting cells into the body. They will naturally to straight to the injury and help heal it. A system of injections without needles could also slow the ageing process by using the same process to "tune" cells. Bruce Lahn, professor of human genetics at the University of Chicago, anticipates the ability to produce "unlimited supplies" of transplantable human organs without the needed a new organ, such as kidney, the surgeon would contact a commercial organ producer, give him the patient"s immuno-logical profile and would then be sent a kidney with the correct tissue type. These organs would be entirely composed of human cells, grown by introducing them into animal hosts, and allowing them to develop into and organ in place of the animal"s own. But Prof. Lahn believes that farmed brains would be "off limits". He says: "Very few people would want to have their brains replaced by someone else"s and we probably don"t want to put a human braining an animal body." Richard Miller, a professor at the University of Michigan, thinks scientist could develop "authentic anti-ageing drugs" by working out how cells in larger animals such as whales and human resist many forms of injuries. He says: "It"s is now routine, in laboratory mammals, to extend lifespan by about 40%. Turning on the same protective systems in people should, by 2056, create the first class of 100-year-olds who are as vigorous and productive as today"s people in their 60s." Spinal injuries Ellen Heber-Katz, a professor at the Wistar Institude in Philadelphia, foresees cures for injuries causing paralysis such as the one that afflicted Superman star Christopher Reeve. She says: "I believe that the day is not far off when we will be able to proscribe drugs that cause severed spinal cords to heal, hearts to regenerate and lost limbs to regrow." "People will come to expect that injured or diseased organs are meant to be repaired from within, in much the same way that we fix an appliance or automobile: by replacing the damaged part with a manufacturer-certified new part." She predicts that within 5 to 10 years fingers and toes will be regrown and limbs will start to be regrown a few years later. Repairs to the nervous system will start with optic nerves and, in time, the spinal cord. "Within 50 years whole body replacement will be routine," Prof. Heber-Katz adds.

单选题Today this dangerous situation has been largely alleviated. Henry, a 77-year-old pensioner from East London, still lives alone and happily practices golf swings in his back garden safe in the knowledge that his body is able to cope with the extra exertion. What has altered Henry's life is not some wonder drug but a simple change in the way his illness is managed. Every day Henry hooks himself up to monitoring devices whose results have helped him to understand it and overcome its more debilitating effects. "Telehealth has given me confidence in myself because I know my own body now, " he says. He adjusts what he does according to what his daily readings tell him about his condition. Henry is just one of a growing number of pioneering patients who are trusting their futures to telehealth. Large trials are under way around the world to evaluate the idea. With elderly populations and the incidence of age-related illnesses growing telehealth promises to give people the independence they need to remain in their own homes. It could also reduce the burden of healthcare costs. The disorder that makes Henry's life so difficult is chronic obstructive pulmonary disease (COPD), a condition that affects some 800, 000 people in England. The airways in his lungs have narrowed, leaving him with severe shortness of breath and blood oxygen levels that can fall dangerously low. With his new equipment, Henry can keep a close eye on how his body is doing. He received for measuring his blood oxygen level and pulse rate, a blood pressure monitor and a set of speaking scales. Each connects wirelessly to a unit which collates the readings and sends them to a team of medical specialists, who watch for suspicious changes. If the readings look bad, they call him to discuss appropriate action. Henry too can see the readings on his television, where they are displayed with the help of a special set-top box. Whether a day is good or bad depends largely on Henry's blood oxygen level. Before joining the telehealth program, he could only guess at that. Now he knows if the reading is low, he can take action. When the reading is high, he can go about his business confident that his oxygen level will see him through. "Telehealth is a good thing for me, " says Henry. "I know that on the other end of the telephone there's a little angel and if anything goes wrong it shows up on the television and she's on the phone within five minutes. "

单选题People have worried about smog for many years, and the government has spent billions of dollars to try to clean up the air of big cities. Now we find that there is no escape from unhealthful air. Recent studies have shown that air inside many homes, office buildings, and schools is full of pollutants; chemicals, bacteria, smoke, and gases. These pollutants are causing a group of unpleasant and dangerous symptoms that experts call "sick building syndrome". A "sick building" might be a small house in a rural area or an enormous office building in an urban center. A recent study reached a surprising conclusion: Indoor air pollution is almost always two to five times worse than outside pollution! This is true even in buildings that are close to factories that produce chemicals. The solution to this problem would seem very clear; Open your windows and stay out of modern office buildings with windows that don't open. Unfortunately, the solution might not be so simple, better ventilation—a system for moving fresh air—can cut indoor air pollution to a safe level, but lack of ventilation is seldom the main cause of the problem. Experts have found that buildings create their own pollution. Imagine a typical home. The people who live there burn oil, wood, or gas for cooking and heating. They might smoke cigarettes, pipes, or cigars. They use chemicals for cleaning. They use hundreds of products made of plastic or particle board; these products—such as the shelves in Oakland High School— give off chemicals that we can' t see but that we do breathe in. And in many areas, the ground under the building might send a dangerous gas called radon into the home. The people in the house are breathing in a "chemical soup" , and medical experts don't yet know how dangerous this is for the human body.

单选题People are extraordinarily skilled at spotting cheats — much better than they are at detecting rule-breaking that does not involve cheating. A study showing that just how good we are at this adds weight to the theory that our exceptional brainpower arose through evolutionary pressures to acquire specific cognitive skills. The still-controversial idea that humans have specialized decision systems in addition to generalized reasoning ability has been around for decades. Its advocates point out that the ability to identity untrustworthy people should be favored evolutionally since cheats risk undermining the social interactions in which people trade goods or services for mutual benefit. To test whether we have a special ability to reason about cheating, Leda Cosmides, an evolutionary psychological test called the Wason selection test, which tests volunteers' ability to reason about "if/then" statements. The researchers set up scenarios in which they asked undergraduate volunteers to imagine they were supervising workers sorting applications for admission to two schools: a good one in a district where school taxes are high, and a poor one on an equally wealthy, but lightly taxed district. The hypothetical workers were supposed to follow a rule that specified "if a student is admitted to the good school, they must live in the highly taxed district". Half the time, the test subjects are told that the workers had children of their own applying to the schools, thus having a motive to cheat; the rest of the time they were told the workers were merely absent-minded and sometimes made innocent errors. Then the test subjects were asked how they would verify that the workers were not breaking the rule. Cosmides found that when the "supervisors" thought they were checking for innocent errors, just 9 of 33, or 27 percent, got the right answer—looking for a student admitted to the good school who did not live in the highly-taxed district. In contrast, when the supervisors thought they were watching for cheats, they did much better with 23 of 34, or 68 percent getting the right answer. This suggests that people are, indeed more adept at spotting cheat than at detecting mere rule-breaking. Cosmides says, "Any cues that it's just an innocent mistake actually inactivate the detection mechanism. " The result is what you would expect if natural selection had favored this specific ability in early, pro-social humans — and is not at all what would happen under selection for generalized intelligence, Cosmides says. "My claim is that there is nothing domain-general in the mind, just that that can't be the only thing going on in the mind. " Other psychologists remain skeptical of this conclusion. "If you want to conclude that therefore there's a module in the mind for detecting cheater, I see zero evidence for that, " says Steven Sloman, a cognitive scientist at Brown University in Providence, Rhode Island. "It's certainly possible that it's something we learned through experience. There is no evidence that it's anything innate. "

单选题Some futurologists have assumed that the vast upsurge of women in the workforce may portend a rejection of marriage. Many women, according to this hypothesis, would rather work than marry. The converse of this concern is that the prospects of becoming a multi-paycheck household could encourage marriage. In the past, only the earnings and financial prospects of the man counted in the marriage decision. Now, however, the earning ability of a woman can make her more attractive as a marriage partner. Data show that economic downturns tend to postpone marriage because the parties cannot afford to establish a family or are concerned about rainy days ahead. As the economy rebounds, the number of marriages also rises. Coincident with the increase in women working outside the home is the increase in divorce rates. Yet, it may be wrong to jump to any simple cause-and-effect conclusions. The impact of a wife"s work on divorce is no less cloudy than its impact on marriage decisions. The realization that she can be a good provider may increase the chances that a working wife will choose divorce over an unsatisfactory marriage. But the reverse is equally plausible. Tensions grounded in financial problems often play a key role in ending a marriage. Given high unemployment, inflationary problems, and slow growth in real earnings, a working wife can increase household income and relieve some of these pressing financial burdens. By raising a family"s standard of living, a working wife may strengthen her family"s financial and emotional stability. Psychological factors also should be considered. For example, a wife blocked from a career outside the home may feel caged in the house. She may view her only choice as seeking a divorce. On the other hand, if she can find fulfillment through work outside the home, work and marriage can go together to create a stronger and more stable union. Also, a major part of women"s inequality in marriage has been due to the fact that, in most cases, men have remained the main breadwinners. With higher earning capacity and status occupations outside of the home comes the capacity to exercise power within the family. A working wife may rob a husband of being the master of the house. Depending upon how the couple reacts to these new conditions, it could create a stronger equal partnership or it could create new insecurities.

单选题Visual impairment carries with【C1】______ ability to travel through one's physical and social until adequate orientation and mobility skills have been established. Because observational skills are more limited, self-control within the immediate surroundings is limited. The visually impaired person is less able to anticipate【C2】______ situations or obstacles to avoid. Orientation refers to the【C3】______ map one has of one's surroundings and to the relationship between self and that environment. It is best generated by moving through the environment and【C4】______ together relationships, object by object, in an organized approach. With【C5】______ visual feedback to reinforce this map, a visually impaired person must rely on memory for key landmarks and other clues, which enable visually impaired persons to【C6】______ their position in space. Mobility is the ability to travel safely and efficiently from one point to another within one's physical and social environment. Good orientation skills are necessary to good mobility skills. Once visually impaired students learn to travel safely as pedestrians (行人), they also need to learn to use public transportation to become as【C7】______ as possible. To meet the【C8】______ demands of the visually impaired person, there is a sequence instruction that begins during the preschool years and may continue after high schools. Many visually impaired children lack adequate concepts regarding time and space or objects and events in their environment. During the early years much attention is focused on the development of some fundamental【C9】______ , such as inside or outside, in front of or behind, fast or slow, which are essential to safe,【C10】______ travel through familiar and unfamiliar settings.

单选题Every year, the American Lung Association(ALA)releases its annual report card on smog, and every year it gives "F" to over half the nation"s counties and cities. When ALA"s "state of the Air 2002" recently came out, dozens of credulous local journalists once again took the habit, ominously reporting that their corner of the nation received a failing grade. The national coverage was no better, repeating as fact ALA"s statement that it is "gravely concerned" about air quality, and neglecting to solicit the views of even one scientist with a differing view. Too bad, because this report card says a lot less about actual air quality than it does about the tactics and motives of the ALA. The very fact that 60 percent of counties were given an "F" seems to be alarmist. This is particularly true given that smog levels have been trending downward for several decades. According to the Environmental Protection Agency(EPA)statistic, ozone, the primary constituent of smog, has declined by approximately 30 percent since the 1970s. And recent gains indicate that the progress will likely continue, even without the wave of new regulations ALA is now demanding. ALA is correct that some areas still occasionally exceed the federal standard for ozone, but such spikes are far less frequent than in the past. Even Los Angeles, the undisputed smog capital of America, has cleaned up its act considerably. Los Angles, which exceeded federal smog standards for 154 days in 1989, has had 75 percent fewer such spikes in recent years. But an ALA-assigned "F" misleadingly implies that air quality are not improved at all. Most of the nation currently in attainment with the current smog standard, and much of the rest is getting close. Nonetheless, ALA chose to assign an "F" to an entire country based on just a few readings above a strict new EPA standard enacted in 1997 but not yet in force. In effect, ALA demanded a standard even more stringent than the federal government"s, which allows some leeway for a few anomalously high readings in otherwise clean areas. ALA further exaggerated the public health hazard by grossly overstating the risk of these relatively minor and sporadic increases above standard.

单选题Cholesterol plays a key role in the development of embryo cells, biologists have discovered. They say that this much maligned fatty molecule, best known for its links to heart disease, helps to position a family of "controller" proteins that tell embryo cells how they should form. In laboratory studies on fruit flies and mice, Phil Beachy and his colleagues at Johns Hopkins University in Baltimore looked at members of a family of controller proteins known as Hedgehog. Fruit fly embryos that lack the genes for these proteins develop a spiky appearance — hence the name. Biologists already know that Hedgehog proteins help to direct the development of embryo cells by delivering signals at the cell surface. The proteins only deliver their signals when they split in two, and one half binds to a lipid, a fatty molecule. Beachy" s team discovered that this lipid is cholesterol. In previous test-tube experiments, scientists have found that the concentration and distribution of Hedgehog proteins on the surface of embryo cells can be critical in determining their fate. For example, cells taken from the embryonic nervous system become motor neurons when exposed to low concentrations of Hedgehog proteins, while at high concentrations they turn into structural cells known as floor plates. Until now, however, no one knew what determined the concentration of the proteins on the surface of cells in the embryo. Beachy" s findings suggest that cholesterol" s role is to allow the signaling proteins to enter cells. Since the lipid molecule is water-hating or hydrophobic, the researchers argue, it may act as a key, allowing the Hedgehog proteins to move through the hydrophobic membranes of target cells, or to stick to them. The results appear in the current issue of Science. Researchers already know that cholesterol does some important jobs: for example, it is involved in the production of hormones and is vital for fertility and for the healthy membrane structure of cells. Beachy" s latest results show that cholesterol is also needed for embryonic development. They also help to explain a long-known but mysterious finding that pregnant rats given drugs that block the manufacture of cholesterol produce deformed fetuses. Gail Martin, a developmental biologist at the University of California, San Francisco, describes the findings as "exciting". They may also have wider implications, she says: it is likely that cholesterol" s action is needed more generally for signaling between cells. Beachy too believes that the findings may have "strong connections for human biology". For example, they throw light on a birth disorder that has been linked to the mother" s inability to make cholesterol. This disorder, Smith-Lemli-Opitz syndrome, affects about 1 in 9000 newborn babies, causing defects such as small head size.

单选题Dr. Beatrice Hahn of the University of Alabama at Birmingham announced that she" d learned the origins of HIV-1, the virus responsible for 99 percent of the world" s 33million AIDS cases. Hahn and her colleagues were able to trace it specifically to a subspecies of chimpanzee called Pan troglodytes. Chimps are not the only primates that carry viruses related to HIV. Earlier this decade scientists linked HIV-2 to a monkey called the sooty mangabey. Mandrills and African green monkeys carry still other simian immuno-deficiency viruses(SIVs). The closest links to HIV-1 seemed to be three viral samples isolated in chimpanzees. But one of the three was so divergent from the other two that scientists doubted they were HIV-1" s immediate ancestors. To solve this puzzle, Hahn and her international team first had to fit the human and simian viruses into genetic "family trees" that accounted for their similarities and differences. They next had to show that the chimps were in the same region where AIDS got its start in humans. In fact, the chimp subspecies lives in West Central Africa, the region where HIV-1 is thought to have originated. There was even a plausible mode of transmission from chimp to human. The animals have long been hunted for food, so blood from the carcasses could easily have entered the hunters" bodies through superficial wounds. Hahn"s group showed how, after jumping species on at least three occasions, chimpanzee SIV evolved into the three families of HIV-1 strains recognized today. The question is not merely of academic interest. The chimps, it seems, carry their version of the virus but do not get sick from it. In theory at least, they could reveal important clues about controlling AIDS. "Humans share 98.5 percent of their genes with chimpanzees, points out Dr Feng Gao of UAB, one of Hahn" s collaborators. But just as scientists are learning the chimps" value in AIDS research, this critical subpopulation is being hunted to the brink of extinction. Not only does that mean hunters may be contracting additional viral strains; it also means that mankind is losing a living data-base of AIDS information. "It" s like burning a whole library of books without having read them," says Hahn. Given the similarity of man and chimp, it could prove a tragic loss. Who knows what other mysteries may be answered in those books.

单选题Women find a masculine face—with a large jaw and a prominent brow—-more attractive when they are most likely to attractive, according to a study published in the June 24 NATURE. Before, during, and use after menstruation, however, they seem to be drawn to less angular, more "feminine" male faces, the researchers report. " Other studies of female preference, mainly for odors, show changes across the menstrual cycle ," says lead author Ian Penton-Voak of the University of St. Andrews in Scotland. " We thought it would be interesting to look at visual preferences and see if they changed also". The researchers showed 39 Japanese women composite male faces that emphasized masculine or feminine facial features to differing degrees. The women preferred images with more masculine features when they were in the fertile phase of their menses but favored more feminine features during their less fertile phase. The type of face women find attractive also seems to depend on the kind of relationship they wish to pursue, according to another experiment. The cyclic preference for muscular faces was evident among 23 British women asked to choose the most attractive face for a short-term relationship, Penton-Voak says. The 26 women asked to choose an attractive face for a long-term relationship, however, preferred the more feminine features throughout their menstrual cycle. Another 22 women who were using oral contraceptives did not show monthly changes in the faces they preferred even for short-term relationships, indicating that hormones might play a role in determining attractiveness, Penton-Voak says. Men whose faces have some feminine softness are perceived as " kinder" men who may make better husbands and partners, he adds, while macho features may be associated with higher testosterone(睾丸素)levels and good genes. He cautions, however, that research hasn"t yet shown a link between a woman" s preferences in such tests and her actual behavior.

单选题Although biological mechanisms do not work with the accuracy or stability of modern clocks, a sense of time and its rhythm is built into the functioning of the human body. Our heart, with its beating pulse, is the clocklike internal rhythm of which we are most aware. In his discovery of the law of the pendulum, which turned out to have the most profound effect on all later time—measuring devices, Galileo used—if legend can be believed—his own pulse beat as the test. There are, however, other biological timekeepers that play important roles in our lives. These inner clocks are generally very regular, but they can also be "reset" and will fall in step with a shifted rhythm. Even after we take a long flight across the Atlantic or Pacific, our lack of synchronization with the local time slowly disappears. The technical term, introduced in 1959, for the internal timer that keeps track of this 24-hour periodicity and retains it even in the absence of external cues is the circadian system (from the Latin circa for "about" or "approximately" and dies for "day"). Though known to biologists for over 200 years, biological clocks have been the subject of intensive research during the last half century. The first human physiological variables that scientists observed to be governed by a circadian rhythm were pulse rate and body temperature. Even if a person rests in bed and fasts, his or her deep-body temperature will vary by almost one degree centigrade between its low in the early morning hours and a high late in the afternoon. More than 100 additional physiological and psychological variables are also subject to diurnal periodicities. For example, the speed with which children can do computations varies by about 10 percent between its slowest value in the early morning to a high before noon, dropping to a nadir in the early afternoon, rising again to a peak at about 6 o' clock and then falling off in the evening. This pattern was first measured in 1907 and replicated a half century later. The extremely controversial question that arose immediately was to what extent this human circadian rhythm was an autonomous mechanism rather than a simple response to external signals, such as changes in the level of light, the times of meals, or social interactions with our surroundings. It has not been easy to find the answer, but careful laboratory experiments have led to the definite conclusion that our body contains an autonomous timekeeper. Individuals who volunteered to be kept in artificial isolation with no time cues of any kind also helped find the answer. In 1962 a French researcher spent two months in a cold cave, 375 feet underground in the Alps. The Frenchman called his aboveground supporters by telephone whenever he ate, went to sleep, and woke, and he recorded in detail his thoughts and impressions of the passage of time. He and all such explorers found themselves subject to definite internal time signals. It turned out, however, that the measured period of their bodily variables (all of which were consistent with one another), as well as their subjective impression of the time of day and their periods of sleep and waking , was slightly longer than 25 hours. By the time they emerged from their prolonged isolation, their internal timer was many hours out of phase with the external 24-hour clock. Today, the autonomy of biological clocks is a well-established fact. Though running at a steady rate, our internal clock is "slow" by about an hour per day, but since it is continually automatically reset by cycles of light and dark, under normal circumstances the loss of time is not cumulative, our internal clock is entrained with the rhyme of the Sun.

单选题Cancer is the second leading cause of death in the United States, after heart disease. In the past, it was often considered a death sentence. But many patients now live longer【C1】______of improvements in discovery and treatment. Researchers say death【C2】______in the United States from all cancers combined have fallen for thirty years. Survival rates have increased for most of the top fifteen cancers in both men and women, and for cancers in【C3】______. The National Cancer Institute and the Centers for Disease Control and Prevention studied the number of cancer survivors. A cancer survivor is defined【C4】______anyone who has been found to have cancer. This would include current patients. The study covered the period from 1971 to 2001. The researchers found there are three【C5】______as many cancer survivors today as there were thirty years ago. In 1971, the United States had about threemillion cancer survivors. Today there are about tenmillion. The study also found that 64% of adults with cancer can expect to still be【C6】______in five years. Thirty years ago, the five-year survival rate was 50%. The government wants to【C7】______the five-year survival rate to 70% by 2010. The risk of cancer increases with age. The report says the majority of survivors are 65 years and older. But it says medical improvements have also helped children with cancer live【C8】______longer. Researchers say 80% of children with cancer will survive at least five years after the discovery. About 75% will survive at【C9】______ten years. In the 1970s, the five-year survival rate for children was about 50%. In the 1960s, most children did not survive cancer. Researchers say they expect more improvements in cancer treatment in the future. In fact, they say traditional cancer-prevention programs are not enough anymore. They say public health programs should also aim to support the【C10】______numbers of cancer survivors and their families.