单选题Osteoporosis used to be called "the silent disease" because its victims didn" t know they had it until it was too late and they suffered a bone fracture. Today, doctors can identify osteoporosis early. Improved understanding of the disease has also led to new treatments and strategies for preventing the disease altogether. For post-menopausal women, the most common medical response to osteoporosis is hormone replacement therapy. Boosting estrogen levels strengthens the entire skeleton and reduces the risk of hip fracture. Unfortunately, it sometimes causes uterine bleeding and may increase the risk of breast cancer. To bypass such side effects, researchers have developed several alternative treatments. Synthetic estrogens called Selective Estrogen Receptor Modulators(SERMs)emulate estrogen with slight modifications. Another drug, alendronate, reduces spine, hip and wrist fractures by 50 percent. Researchers have even developed a nasal spray called calcitonin. Each of these alternatives has trade-offs, however. Patients must talk with their doctors to decide which therapy is best for them. The ideal way to address osteoporosis is by adopting a healthy lifestyle. And the best time to do this is in childhood, when most bone mass is accumulated. Because bodies continue building bone until about age thirty, some experts believe that women in their twenties can still increase their bone strength by as much as 20 percent. Calcium, which is available in low-fat dairy foods and dark green vegetables, is essential for preventing osteoporosis. So is vitamin D, which aides calcium absorption. Vitamin D comes from sunlight, but dietary supplements may be helpful in northern climates and among those who don"t get outside. The final component is regular moderate exercise because bone responds to the needs that the body puts on it. These are the simple steps that can help make "the silent disease" truly silent.

单选题It is common to think that other animals are ruled by instinct whereas humans lost their instincts and ruled by reason, and that this is why we are so much more flexibly intelligent than other animals. William James, in his book Principles of Psychology, took the opposite view. He argued that human behavior is more flexibly intelligent than that of other animals because we have more instincts than they do, not fewer. We tend to be blind to the existence of these instincts, however, precisely because they work so well—because they process information so effortlessly and automatically. They structure our thought so powerfully, he argued, that it can be difficult to imagine how things could be otherwise. As a result, we take normal behavior for granted. We do not realize that normal behavior needs to be explained at all. This instinct blindness makes the study of psychology difficult. To get past this problem, James suggested that we try to make the natural seem strange. It takes a mind debauched by learning to carry the process of making the natural seem strange, so far as to ask for the why of an instinctive human act. In our view, William James was right about evolutionary psychology. Making the natural seem strange is unnatural—it requires the twisted outlook seen, for example, in Gary Larson cartoons. Yet it is a central part of the enterprise. Many psychologists avoid the study of natural competences, thinking that there is nothing to be explained. As a result, social psychologists are disappointed unless they find a phenomenon that would surprise their grandmothers and cognitive psychologists spend more time studying how we solve problems we are bad at, like learning math or playing chess, than ones we are good at. But our natural competences—our abilities to see, to speak, to find someone beautiful, to reciprocate a favor, to fear disease, to fall in love, to initiate an attack, to experience moral outrage, to navigate a landscape, and myriad others—are possible only because there is a vast and heterogeneous array of complex computational machinery supporting and regulating these activities. This machinery works so well that we don't even realize that it exists—we all suffer from instinct blindness. As a result, psychologists have neglected to study some of the most interesting machinery in the human mind.

单选题In patients with Huntington" s disease, it" s the part of the brain called the basal ganglia that" s destroyed. While these victims have perfectly intact explicit memory systems, they can"t learn new motor skills. An Alzheimer" s patient can learn to draw in a mirror but can" t remember doing it: a Huntington" s patient can" t do it but can remember trying to learn. Yet another region of the brain, an almond-size knot of neural tissue seems to be crucial in forming and triggering the recall of a special subclass of memories that is tied to strong emotion, especially fear. These are just some of the major divisions. Within the category of implicit memory, for example, lie the subcategories of associative memory—the phenomenon that famously led Parlov" s dogs to salivate at the sound of a bell which they had learned to associate with food and of habituation, in which we unconsciously file a-way unchanging features of the environment so we can pay closer attention to what" s new and different upon encountering a new experience. Within explicit, or declarative memory, on the other hand, there are specific subsystems that handle shapes, textures such as faces, names—even distinct systems to remember nouns vs. verbs. All of these different types of memory are ultimately stored in the brain" s cortex, within its deeply furrowed outer layer—a component of the brain dauntingly more complex than comparable parts in other species. Experts in brain imaging are only beginning to understand what goes where, and how the parts are reassembled into a coherent whole that seems to be a single memory is actually a complex construction. Think of a hammer, and your brain hurriedly retrieves the tool" s name, its appearance , its function, its heft and the sound of its clang, each extracted from a different region of the brain. Fail to connect person" s name with his or her face, and you experience the breakdown of that assembly process that many of us begin to experience in our 20s and that becomes downright worrisome when we reach our 50 s. It was this weakening of memory and the parallel loss of ability to learn new things easily that led biologist Joe Tsien to the experiments reported last week. " This age-dependent loss of function. " he says, "appears in many animals, and it begins with the onset of sexual maturity. " What" s happening when the brain forms memories—and what fails with aging, injury and disease—involves a phenomenon known as "plasticity". It" s obvious that something in the brain changes as we learn and remember new things, but it" s equally obvious that the organ doesn" t change its overall structure or grow new nerve cells wholesale. Instead, it" s the connections between new cells—and particularly the strength of these connections that are altered by experience. Hear a word over and over, and the repeated firing of certain cells in a certain order makes it easier to repeat the firing pattern later on. It is the pattern that represents each specific memory.

单选题Humanity has passed a milestone: more people live in cities than in rural areas. The current rate of urbanization is unprecedented in our history. In 1950, only 29% of people lived in cities, by 2050, 70% are projected to do so — most of them in poorer countries. Among many other issues, this rapid concentration makes cities a front line in the battles against climate change and pollution. Confronting the challenges of rampant urbanization demands integration multidisciplinary approaches, and new thinking. Take the building boom associated with the increased wealth of urban areas, and its impact on greenhouse-gas emissions as example. In China alone, the United Nations Environmental Program estimates the energy demand for heating homes build over the next decade could increase by some 430 terawatt-hours, or 4% of China's total energy use in 2003. Worldwide, the energy consumed by buildings already accounts for around 45% of greenhouse-gas emissions. Fortunately, researchers in Germany and elsewhere have already shown that they can reduce that energy consumption by 80%-90%, just by overhauling obsolete building designs and using existing technologies. These ultra-efficient buildings demand that planners, architects, engineers and building scientists work together from the outset, and require higher levels of expertise the conventional buildings. But such buildings are often cheaper than those built using conventions methods. Research is also needed to develop technologies, materials and energyconcepts; the green building research today is fragmented and poorly funded. Expanding cities must embrace such technologies and strategies — and not just in the developed nations. Many poorer countries have a rich tradition of adapting buildings to look at practices, environments and climates—a home-grown approach to integrated design that has been all but been lost in the West. They now have an opportunity to combine these traditional approaches with modern technologies. Integrated thinking is also needed to mitigate urban air pollution, which is becoming serious health and environmental risk in many regions—as shown by China's struggle to clean up Beijing's air for the Olympics. Understanding air pollution will require researchers from multiple disciplines, from atmospheric chemistry to meteorology, working over scales from street level to global. And reducing it will require integrated policies for urban planning, transport and housing — not least to reduce the use of cars.

单选题Avian influenza is an infectious disease of birds caused by type A strains of the influenza virus. The disease, which was first identified in Italy more than 100 years ago, occurs worldwide. All birds are thought to be susceptible to infection with avian influenza, though some species are more resistant to infection than others. Infection causes a wide spectrum of symptoms in birds, ranging from mild illness to a highly contagious and rapidly fatal disease resulting in severe epidemics. The latter is known as "highly pathogenic avian influenza". This form is characterized by sudden onset, severe illness, and rapid death, with a mortality that can approach 100%. Fifteen subtypes of influenza virus are known to infect birds, thus providing an extensive reservoir of influenza viruses potentially circulating in bird populations. To date, all outbreaks of the highly pathogenic form have been caused by influenza A viruses of subtypes H5 and H7. Migratory waterfowl — most notably wild ducks — are the natural reservoir of avian influenza viruses, and these birds are also the most resistant to infection. Domestic poultry, including chickens and turkeys, are particularly susceptible to epidemics of rapidly fatal influenza. Direct or indirect contact of domestic flocks with wild migratory waterfowl has been implicated as a frequent cause of epidemics. Live bird markets have also played an important role in the spread of epidemics. Recent research has shown that viruses of low pathogenicity can, after circulation for sometimes short periods in a poultry population, mutate into highly pathogenic viruses. During a 1983-1984 epidemic in the United States of America, the H5N2 virus initially caused low mortality, but within six months became highly pathogenic, with a mortality approaching 90%. Control of the outbreak required destruction of more than 17 million birds at a cost of nearly US$ 65 million. During a 1999-2001 epidemic in Italy, the H7N1 virus, initially of low pathogenicity, mutated within 9 months to a highly pathogenic form. More than 13 million birds died or were destroyed. The quarantining of infected farms and destruction of infected or potentially exposed flocks are standard control measures aimed at preventing spread to other farms and eventual establishment of the virus in a country's poultry population. Apart from being highly contagious, avian influenza viruses are readily transmitted from farm to farm by mechanical means, such as by contaminated equipment, vehicles, feed, cages, or clothing. Highly pathogenic viruses can survive for long periods in the environment, especially when temperatures are low. Stringent sanitary measures on farms can, however, confer some degree of protection. In the absence of prompt control measures backed by good surveillance, epidemics can last for years. For example, an epidemic of H5N2 avian influenza, which began in Mexico in 1992, started with low pathogenicity, evolved to the highly fatal form, and was not controlled until 1995.

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, research over the past few decades has produced(or suggested)some importance in prevention, screening or treatment. 【C3】______however, we consider not what researcher 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Since the first brain scanner was constructed several years ago, computed tomography or computed medical imagery, has become fairly widely used. Its rapid acceptance is due to the fact that it has overcome several of the drawbacks of conventional X-ray technology. To begin with, conventional two-dimensional X-ray pictures cannot show all of the information contained in a three-dimensional object. Things at different depths are super imposed, causing confusion to the viewer. Computed tomography can give three-dimensional information. The computer is able to reconstruct pictures of the body's interior by measuring the varying intensities of X-ray beams passing through sections of the body from hundreds of different angles. Such pictures are based on series of thin "slices". In addition, conventional X-ray generally differentiates only between bone and air, as in the chest and lungs. They cannot distinguish soft tissues or variations in tissues. The liver and pancreas are not discernible at all, and certain other organs max only be rendered visible through the use of radio paque dye. Since computed tomography is much more sensitive, the soft tissues of the kidneys or the liver can be seen and clearly differentiated. This technique can also accurately measure different degrees of X-ray absorption, facilitating the study of the nature of tissue. A third problem with conventional X-ray methods is their inability to measure quantitatively the separate densities of the individual substances through which the X-ray has passed. Only the mean absorption of all the tissues is recorded. This is not a problem with computed tomography. It can accurately locate a tumor and subsequently monitor the progress of radiation treatment, so that in addition to its diagnostic capabilities, it can play a significant role in therapy.

单选题In a society where all aspects of our lives are dictated by scientific advances in technology, science is the essence of our existence. Without the vast advances made by chemists, physicists, biologists , geologists and other diligent scientists, our standards of living would decline, our flourishing wealthy nation might come to an economic depression, and our people would suffer from diseases that could not be cured. As a society we ignorantly take advantage of the amenities provided by science , yet our lives would be altered interminably without them. Health care, one of the aspects of our society that separates us from our archaic ancestors, is founded exclusively on scientific discoveries and advances. Without the vaccines created by doctors , diseases such as polio, measles, hepatitis, and the flu would pose a threat to our citizens, for although some of these diseases may not be deadly, their side effects can be a vast detriment to an individual affected with the disease. In addition, science has developed perhaps the most awe-inspiring vital invention in the history of the world, the computer. Without the presence of this machine our world could exist, but the conveniences brought into life by the computer are unparalleled. Despite the greatness of present-day innovators and scientism and their revelations, it is requisite to examine the amenities of science that our culture so blatantly disregards. For instance, the light bulb, electricity, the telephone, running water, and the automobile are present-day staples of our society, however, they were not present until scientists discovered them. Because of the contribution of scientists, our world is ever metamorphosing, and this metamorphosis economically and personally comprises our society, whether our society is cognizant of this or not.

单选题Information technology that helps doctors and patients make decisions has been around for a long time. Crude online tools like WebMD get millions of visitors a day. But Watson is a different beast. According to IBM, it can digest information and make recommendations much more quickly, and more intelligently, than perhaps any machine before it—processing up to 60 million pages of text per second, even when that text is in the form of plain old prose, or what scientists call "natural language". That's no small thing, because something like 80 percent of all information is "unstructured." In medicine, it consists of physician notes dictated into medical records, long-winded sentences published in academic journals, and raw numbers stored online by public-health departments. At least in theory, Watson can make sense of it all. It can sit in on patient examinations, silently listening. And over time, it can learn and get better at figuring out medical problems and ways of treating them the more it interacts with real cases. Watson even has the ability to convey doubt. When it makes diagnoses and recommends treatments, it usually issues a series of possibilities, each with its own level of confidence attached. Medicine has never before had a tool quite like this. And at an unofficial coming-out party in Las Vegas last year, during the annual meeting of the Healthcare Information and Management Systems Society, more than 1 000 professionals packed a large hotel conference hall, and an overflow room nearby, to hear a presentation by Marty Kohn, an emergency-room physician and a clinical leader of the IBM team training Watson for health care. Standing before a video screen that dwarfed his large frame, Kohn described in his husky voice how Watson could be a game changer—not just in highly specialized fields like oncology but also in primary care, given that all doctors can make mistakes that lead to costly, sometimes dangerous, treatment errors. Drawing on his own clinical experience and on academic studies, Kohn explained that about one-third of these errors appear to be products of misdiagnosis, one cause of which is "anchoring bias": human beings' tendency to rely too heavily on a single piece of information. This happens all the time in doctors' offices, clinics, and emergency rooms. A physician hears about two or three symptoms, seizes on a diagnosis consistent with those, and subconsciously discounts evidence that points to something else. Or a physician hits upon the right diagnosis, but fails to realize that it' s incomplete, and ends up treating just one condition when the patient is, in fact, suffering from several. Tools like Watson are less prone to those failings. As such, Kohn believes, they may eventually become as ubiquitous in doctors' offices as the stethoscope. "Watson fills in for some human limitations," Kohn told me in an interview. "Studies show that humans are good at taking a relatively limited list of possibilities and using that list, but are far less adept at using huge volumes of information. That's where Watson shines; taking a huge list of information and winnowing it down."

单选题Despite growing numbers of joggers, Canada Fitness Surveys across the country demonstrate that Canadians are less physically fit than their U. S. or Swedish counterparts. Many people were【C1】______that they do not exercise often or vigorously enough for optimal benefits. Only about 25 per cent of Canadian adults paddle【C2】______the recommended level that increases the heart beat to a target level【C3】______there for at least 15 minutes thrice weekly. Men are more likely to be either "sedentary" or "very active" , while women are【C4】______to be "moderately active". Common reasons【C5】______are no willpower, poor facilities, boredom, fatigue, no partner, sheer laziness or lack of lime. Experts【C6】______that better use of available time is the answer, with incentives and rewards to help sustain the exercise habit until the benefits become so【C7】______that activity is automatically scheduled into daily routines. A modest increase in daily activity【C8】______the sedentary could improve the overall health of our population more than increased activity in those already dedicated to exercise. Activity in older people helps them【C9】______agile, work and feel better. Many elderly people who remain active have a lower-heart rate than inactive youngsters.【C10】______, one famous marathoner(Clarence Demar), e-ven after age 60, was in better shape than【C11】______Currently only 35 per cent of the over【C12】______take regular walks. Even a small gain in fitness among the elderly may permit them to replace a restricted lifestyle with【C13】______in which they can play golf, dance, cycle and【C14】______The overall【C15】______is clear; physical activity benefits body and mind, and should be encouraged for all, especially those who are now the least active.

单选题American researchers are working on three antibodies that many mark a new step on the path toward an HIV vaccine, according to a report published online Thursday, July 8, 2010, in the journal Science. One of the antibodies suppresses 91 percent of HIV strains, more than any AIDS antibody ever discovered, according to a report on the findings published in the Wall Street Journal. The antibodies were discovered in the cells of a 60-year-old African-American gay man whose body produced them naturally. One antibody in particular is substantially different from its precursors, the Science study says. The antibodies could be tried as a treatment for people already infected with HIV, the WSJ reports. At the very least, they might boost the efficacy of current antiretroviral drugs. It is welcome news for the 33 million people the United Nations estimated were living with AIDS at the end of 2008. The WSJ outlines the painstaking method the team used to find the antibody amid the cells of the African-American man, known as Donor 45. First they designed a probe that looks just like a spot on a particular molecule on the cells that HIV infects. They used the probe to attract only the antibodies that efficiently attack that spot. They screened 25 million of Donor 45's cell to find just 12 cells that produced the antibodies. Scientists have already discovered plenty of antibodies that either don't work at all or only work on a couple of HIV strains. Last year marked the first time that researchers found "broadly neutralizing antibodies, " which knock out many HIV strains. But none of those antibodies neutralized more than about 40 percent of them, the WSJ says. The newest antibody, at 91 percent neutralization, is a marked improvement. Still, more work needs to be done to ensure the antibodies would activate the immune system to produce natural defenses against AIDS, the study authors say. They suggest three test methods that blend the three new antibodies together in raw form to prevent transmission of the virus, such as from mother to child; in a microbicide gel that women or gay men could use before sex to prevent infection; or as a treatment for HIV/AIDS, combined with antiretroviral drug. If the scientists can find the right way to stimulate production of the antibodies, they think most people could produce then, the WSJ says.

单选题What we don't know about kids and television could fill a weeklong miniseries. Given worries about everything from childhood obesity to scholastic shortcomings, it's high time to find out. But before Congress approves $20 million a year to research children and the media, it should get more specific assurances that the money will pay for comprehensive, high-quality studies instead of bits of teasing information. Up to now, a patchwork of research on kids and TV has yielded plenty of suspicion but little real knowledge. Yes, a study two years ago found that teenagers who watched a lot of TV tended to be more aggressive. But what does that mean? Maybe more-aggressive kids are drawn more to TV. Ditto for the April study about preschoolers who watch hours of TV tending to have attention-span problems later on. It's possible that children with a propensity toward attention problems are drawn more to that jumpy on-screen world in the first place. For better or worse, U. S. kids spend a lot of time in front of a TV or computer screen, two hours daily for those 5 and younger. If the schools spent two hours a day on a single activity, there would be intense concern about its value. So there is worth in legislation by Sen. Joe Lieberman to provide $100 million over five years for research on child development and electronic media. A scientific panel would set up a list of the key issues to be studied and review grant applications from universities or nonprofit institutes. This centralized approach makes sense—especially considering the money involved. Good studies are costly, and there haven't been enough of them on this subject. Merely showing a link between TV viewing and a certain behavior doesn't prove anything. In addition to the possibility the behavior is causing the TV watching instead of the other way around, a third factor could be causing both. Only carefully controlled studies obtain worthwhile results. At their best, such studies might tell us whether educational computer games for toddlers interrupt the natural development of the brain instead of aiding it, or whether seeing Ronald McDonald cavort on a soccer field makes a child more active or just more likely to crave French fries. Parents could decide limits based on more than instinct. But before spending the money, Congress should insist on a quality of research that will give the public answers about TV instead of more arguments. This shouldn't be a handout to think tanks for more mushy research on a complicated but vital issue.

单选题Scientists have developed a slimming drug that successfully suppresses appetite and results in a dramatic loss of weight without any apparent ill effects. The drug interferes with appetite control and prevents the build-up of fatty tissue. More importantly, the drug appears to prevent a serious decline in metabolic rate-causing tiredness and lethargy—which is typically associated with living on a starvation diet. As a result, mice taking the drug lost 45 percent more weight than mice fed the same amount of food, which compensate for the lack of food by becoming more sluggish. The scientists, from the Johns Hopkins University in Baltimore, said that C 75 is likely to produce a similar effect on humans because appetite control in the brain is thought to be based largely on the same chemical pathways as those in mice. " We are not claiming to have found the fabled weight-loss drug. What we have found, using C 75, is a major path way in the brain that the body uses naturally in regulating appetite at least in mice," said Francis Kuhajda, a pathologist and senior team member. "We badly need effective drugs for weight loss. Obesity is a huge problem. We"re hoping to explore the possibilities of this new pathway," he said. Discovering a biochemical pathway in the brain that controls appetite raises new prospects for developing slimming aids. Research on leptin, a hormone produced in fatty tissue for controlling fat deposits, has so far failed to produce the expected slimming drug break-through. The latest study, published in the journal Science, showed that even moderate doses of C 75 produced a significant loss of appetite, which returned to normal after a few months. The scientists believe that C 75, which they produced synthetically in the laboratory, binds to an enzyme called fatty acid sythase, which is involved in storing excess food intake as fat. Inhibiting the enzyme causes a build-up of a chemical in the liver which acts as a precursor to fat deposition. This precursor is thought to have an indirect effect on the brain, causing appetite suppression. Normally, when animals fast, a hormone called neuropeptide Y increases sharply in the appetite control centers of the brain, stimulating the desire for food. However, when animals are given C 75, levels of this hormone fall, leading to a loss of interest in food. Dr Kuhajda said discovering that C 75 has no effect on metabolic rate is one of the most significant findings of the study. "If you try to lose weight by starving, your metabolism slows down after a few days," he said. " It" s a survival mechanism that sabotages many diets. We see this in fasting mice. Yet metabolic rate in the C 75-treated mice doesn"t slow at all. " Further animals studies will be needed before C 75 could be tested on humans.

单选题Medical studies show that only two to five percent of the obese manage to shed unwanted pounds permanently. The rest, after intermittent successes, regain or surpass their starting weights within a couple of years. Why do most reducing programs fail in the long run, and so many dieters put back lost weight? Some experts claim that the gloomy estimates of dieting failure may be exaggerated, since some people do manage to keep off at least some weight, even though they may not achieve the svelte look they desire. Only those who fail dismally in their own dieting efforts enter format reduction programs. So, on an optimistic note, some health professionals point out that most studies never consider those who successfully keep weight off, don't seek medical advice and hence aren't counted in the statistics. Another explanation for failure is that diets set up unreal expectations of a magical cure, often based on absurdly monotonous meal plans that cannot possibly be followed for long. And the very idea of dieting implies a temporary effort you go on the new eating regime only to come off it. Once the diet is over and former eating habits taken up again, people often give themselves permission to binge on foods forbidden while dieting. A further obstacle to successful dieting is the exclusion of certain foods that acquire a special status. No food should be forbidden; it is better to work a little ice cream or dessert into your regime to avoid an irresistible urge to gorge on prohibited items. The all too familiar cycle of yo-yo dieting-endless diets followed by weight regain—may leave dieters worse off than before. Some studies suggest that with each successive fast and feast, metabolic changes make the post-dieting weight regained higher in fat than muscle. Repeated dieting often produces depression, a sense of failure, an intense preoccupation with food, loss of self-esteem and stress from the continual deprivation.

单选题Parkinson's disease, first described in the early 1800s by British physician James Parkinson as "shaking palsy", is among the most prevalent neurological disorders. According to the United Nations, at least four million people worldwide have it; in North America, estimates run from 500, 000 to one million, with about 50, 000 diagnosed every year. These figures are expected to double by 2040 as the world's elderly population grows; indeed, Parkinson's and other neurodegenerative illnesses common in the elderly (such as Alzheimer's and amyotrophic lateral sclerosis) are on their way to overtaking cancer as a leading cause of death. But the disease is not entirely one of the aged: 50 percent of patients acquire it after age 60; the other half are affected before then. Furthermore, better diagnosis has made experts increasingly aware that the disorder can attack those younger than 40. So far researchers and clinicians have found no way to slow, stop or prevent Parkinson's. Although treatments do exist — including drugs and deep-brain stimulation — these therapies alleviate symptoms, not causes. In recent years, however, several promising developments have occurred. In particular, investigators who study the role proteins play have linked miscreant proteins to genetic underpinnings of the disease. Such findings are feeding optimism that fresh angles of attack can be identified. As its 19th-century name suggests — and as many people know from the educational efforts of prominent Parkinson's sufferers such as Janet Reno, Muhammad Ali and Michael J. Fox — the disease is characterized by movement disorders. Tremor in the hands, arms and elsewhere, limb rigidity, slowness of movement, and impaired balance and coordination are among the disease's hallmarks. In addition, some patients have trouble walking, talking, sleeping, urinating and performing sexually. These impairments result from neurons dying. Although the victim cells are many and found throughout the brain, those producing the neurotransmitter dopamine in a region called the substantia nigra are particularly hard-hit. These dopaminergic nerve cells are key components of the basal ganglia, a complex circuit deep within the brain that fine-tunes and co-ordinates movement. Initially the brain can function normally as it loses dopaminergic neurons in the substantia nigra, even though it cannot replace the dead cells. But when half or more of these specialized cells disappear, the brain can no longer cover for them. The deficit then produces the same effect that losing air traffic control does at a major airport. Delays, false starts, cancellations and, ultimately, chaos pervade as parts of the brain involved in motor control — the thalamus, basal ganglia and cerebral cortex — no longer function as an integrated and orchestrated unit.

单选题Women do not avoid fighting because they are dainty or scared, but because they have a greater stake than men in staying alive to rear their offspring. Women compete with each other just as tenaciously as men, but with a stealth and subtlety that reduces their chances of being killed or injured, says Anne Campbell of the department of psychology at the University of Durham. Across almost all cultures and nationalities, men have a much smaller role than women in rearing children. "Males go for quantity of children rather than quality of care for offspring, which means that the parental investment of women is much greater," says Campbell. And unlike men, who can" t be sure that their children have not been fathered on the sly by other men, women can always be certain that half an offspring" s genes are theirs. Women have therefore evolved a strong impulse than men to see their children grow up into adults. Men" s psychological approach is geared to fathering as many children as possible. To make this strategy work and to attract partners, men need to establish and advertise their dominance over rival males. Throughout evolution this has translated into displays of male aggression, ranging in scale from playground fights to world wars. Men can afford to take more risks because as parents they are more expendable. Women, meanwhile, can only ensure reproductive success by overseeing the development of their children, which means avoiding death. " The scale of parental investment drives everything," says Campbell. " It" s not that women are too scared to fight," she says. "It" s more to do with the positive value of staying alive, and women have an awfully big stake not just in offspring themselves but in offspring they might have in the future," she says. This means that if women do need to compete—perhaps for a partner—they choose low-risk rules of engagement. They use indirect tactics, such as discrediting rivals by spreading malicious rumors. And unlike men who glory in feats of dominance, women do better by concealing their actions and their "victories". But there is no doubt, says Campbell, that the universal domination of culture by males has exaggerated these differences in attitudes to physical aggression. "The story we" ve always been told is that females are not aggressive," says Campbell. And when they are aggressive; women are told that their behavior is "odd or abnormal".

单选题Flight simulator refers to any electronic or mechanical system for training airplane and spacecraft pilots by simulating flight conditions. The purpose of simulation is not to completely substitute【C1】______actual flight training but to thoroughly familiarize students with the vehicle【C2】______before they undergo extensive and possibly dangerous actual flight training. Two early flight simulators appeared in England within a decade after the first flight of Orville and Wilbur Wright. They were designed to enable pilots to【C3】______simple aircraft maneuvers in three dimensions: nose up or down; left wing high and right low, or vice versa; and yawing to left or right. Until 1929, however, a truly effective simulator, the Link Trainer devised by Edwin A. Link, a self-educated aviator and inventor, appeared.【C4】______, airplane instrumentation had been developed sufficiently to permit " blind" flying on instruments alone, but training pilots to do so involved【C5】______risk. Link built a model of an airplane cockpit equipped【C6】______instrument panel and controls that could simulate all the movements of an airplane. Pilots could use the device for instrument training, manipulating the controls【C7】______instrument readings so as to maintain straight and level flight or controlled climb or descent with no visual reference【C8】______any horizon except for the artificial one on the instrument panel. The trainer was modified【C9】______aircraft technology advanced. Commercial airlines began to use the Link Trainer for pilot training, and the U. S. government began purchasing them in 1934,【C10】______thousands more as World War II approached.

单选题Liver disease is the 12th -leading cause of death in the U. S. , chiefly because once it's determined that a patient needs a new liver it's very difficult to get one. Even in case where a suitable donor match is found, there's no guarantee a transplant will be successful. But researchers at Massachusetts General Hospital have taken a huge step toward building functioning livers in the lab, successfully transplanting culture-grown livers into rats. The livers aren't grown from scratch, but rather within the infrastructure of a donor liver. The liver cells in the donor organ are washed out with a detergent that gently strips away the liver cells, leaving behind a biological scaffold of proteins and extracellular architecture that is very hard to duplicate synthetically. With all of that complicated infrastructure already in place, the researchers then seeded the scaffold (支架) with liver cells isolated from healthy livers, as well as some special endothelial cells to line the bold vessels. Once repopulated with healthy cells, these livers lived in culture for 10 days. The team also transplanted some two-day-old recellularized livers back into rats, where they continued to thrive for eight hours while connected into the rats' vascular systems. However, the current method isn't perfect and cannot seem to repopulate the blood vessels quite densely enough and the transplanted livers can't keep functioning for more than about 24 hours (hence the eight-hour maximum for the rat transplant). But the initial successes are promising, and the team thinks they can overcome the blood vessel problem and get fully functioning livers into rats within two years. It still might be a decade before the tech hits the clinic, but if nothing goes horribly wrong — and especially if stem-cell research establishes a reliable way to create healthy liver cells from the very patients who need transplants — lab-generated livers that are perfect matches for their recipients could become a reality.

单选题During his lifetime Alfred Nobel reaped millions of dollars in profits from his invention and manufacture of high explosives. Some of these greatly increased the killing power of weapons and so made war more terrible. Nobel, nevertheless, left much of his fortune for the promotion of world peace as well as the advancement of scientific knowledge and the encouragement of literary achievement. Alfred Bernhard Nobel was born in Stockholm, Sweden, on Oct. 21, 1833. Alfred was a sickly child. He was educated at home. Instead of going to high school he traveled widely. He learned chemistry and mechanical engineering in private studies and study abroad. At 21, he joined his father and brother in St. Petersburg. The father had begun some experiments with nitroglycerin but had abandoned them. Alfred resumed these experiments and invented a blasting cap, made of fulminate of mercury, to fire a charge of nitroglycerin. The cap was a very important development. Although still sickly, Nobel took charge of the family business. In 1863 he returned to Sweden and set up a small factory to make nitroglycerin. A year later a terrific explosion destroyed the plant and killed five people. One was his youngest brother, Emil. Nobel, however, refused to give up his work and moved the plant to a barge moored in a lake. Further tragedies occurred. In 1866, after disastrous explosions at world ports, many nations forbade their vessels to carry nitroglycerin. Nobel then sought to make the explosive safer to handle. He found the answer in dynamite. The invention made Nobel wealthy. He spent the next ten years setting up plants in the United States and Europe. In 1876 he patented blasting gelatin, a combination of guncotton and nitroglycerin. In 1878 he and his brothers developed oil fields in Russia. He invented ballistite in 1888, one of the first smokeless powders. Nobel never married. He found recreation in his laboratory and in writing poetry in imitation of his idol, Percy Bysshe Shelley. In later years he traveled throughout Europe and had homes in Paris, in Stockholm, and in San Remo, Italy. In 1876 he met Bertha Kinsky(later Baroness von Suttner), a Bohemian noblewoman. In letters to Nobel over several years she developed his ideas for world peace. Nobel" s bequest for a peace prize was largely in tribute to her, though he was somewhat doubtful of the effectiveness of the pacifist movement. He died in 1896 at San Remo, leaving the executors of his will to work out the details of administering the Nobel prizes.

单选题Children are getting so fat they may be the first generation to die before their parents, an expert claimed yesterday. Today"s youngsters are already falling prey to potential killers such as diabetes because of their weight. Fatty fast-food diets combined with sedentary lifestyles dominated by televisions and computers could mean kids will die tragically young, says Professor Andrew Prentice, from the London School of Hygiene and Tropical Medicine. At the same time, the shape of the human body is going through a huge evolutionary shift because adults are getting so fat. Here in Britain, latest research shows that the average waist size for a man is 36-38in and may be 42-44in by 2032. This compares with only 32.6 in in 1972. Women"s waists have grown from an average of 22 inches in 1920 to 24 inches in the Fifties and 30 inches now. One of the major reasons why children now are at greater risk is that we are getting fatter younger. In the UK alone, more than one million under-16s are classed as overweight or obese — double the number in the mid-Eighties. One in ten four-year-olds are also medically classified as obese. The obesity pandemic—an extensive epidemic—which started in the US, has now spread to Europe, Australia, Central America and the Middle East. Many nations now record more than 20 per cent of their population as clinically obese and well over half the population as overweight. Prof Prentice said the change in our shape has been caused by a glut of easily available high-energy foods combined with a dramatic drop in the energy we use as a result of technology developments. He is not alone in his concern. Only last week one medical journal revealed how obesity was fuelling a rise in cancer cases. Obesity also increases the risk factor for strokes and heart disease. An averagely obese person"s lifespan is shortened by around nine years while a severely obese person by many more. Prof Prentice said: "So will parents outlive their children, as claimed recently by an American obesity specialist?" The answer is yes—and no. Yes, when the offspring become grossly obese. This is now becoming an alarmingly common occurrence in the US. Such children and adolescents have a greatly reduced quality of life in terms of both their physical and psychosocial health. So say No to that doughnut and burger.