BSection B/B

BSection B/B

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It is difficult to discern the sample that is on the slide unless the microscope is adjusted properly.

If the cells cannot use sugar, the body begins to______its own tissues for food.

Undoubtedly, I______him as one of the greatest leaders in China" s history.

She was so______in her job that she didn't hear anybody knocking at the door.

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Although he had looked through all the reference material on the subject, he still found it hard to understand this point and her explanation only______to his confusion.

单选题Even as Americans have been gaining weight, they have cut their average fat intake from 36 to 34 percent of their total diets in the past 15 years. And indeed, cutting fat to control or lose weight makes sense. Fat has nine calories per gram. Protein and carbohydrates have just four. Moreover, the body uses fewer calories to metabolize fat than it does to metabolize other foods. Compared with protein and carbohydrates—which break down into amino acids and simple sugars, respectively, and can be used to strengthen and energize the body— dietary fat is more easily converted to body fat. Therefore, it's more likely to stay on buttocks, thighs and bellies. But cutting fat from your diet doesn't necessarily mean your body won't store fat. For example, between nonfat and regular cookies, there's trivial difference in calories because manufacturers make up for the loss of fat by adding sugar. Low-fat crackers, soups and dressings can also be just as high in calories as richer versions. No matter where the calories come from, overeating will still cause weight gain. The calories from fat just do it a little quicker. A Wisconsin computer programmer who decided with a diet coach to eat only 40 grams of fat a day learned the lesson firsthand. He wasn't losing weight. Then he showed his food diary to his coach and revealed he'd been eating half a pound of jelly beans a day. "They don't have any fat, " he explains. But they had enough sugar to keep him from shedding an ounce. Nonfat foods become add-on foods. When we add them to our diet, we actually increase the number of calories we eat per day and gain weight. That was borne out in a Pennsylvania State University study. For breakfast, Prof. Barbara Rolls gave two groups of women yogurt that contained exactly the same amount of calories. One group's yogurt label said "high fat"—the other, "low fat. " The "low fat" yogurt group ate significantly more calories later in the day than the other group. "People think they've saved fat and can indulge themselves later in the day with no adverse consequences, " says Richard Mattes, a nutrition researcher at Purdue University. "But when they do that, they don't compensate very precisely, and they often end up overdoing it. "

单选题Edna was not in the least surprised by my offer. I hitched the traveling-can containing the food on to the carrier. I didn't want to ride on the rough approach to the house so I rolled the bicycle the short distance from the house to the mad while Edna walked beside me. Mounting the vehicle with the can on the back and Edna on the cross-bar proved a little tricky, I solved the problem by getting on the seat first and keeping the bicycle stationary with one foot resting firmly on the ground. Then Edna climbed on the bar sitting sideways; and I pushed off. The excitement of having her so close within my arms and the perfume of her hair in my nose would have proved overpowering if I'd had much time to consider it. I hadn't. The road to the hospital turned out to be quite hilly, not steep but just enough to take the wind out of one ; and with the kind of passenger I had, I didn't care to admit too readily to being tired. So I raced up all the little hillocks until my heart raged like a bonfire. "You are very strong," said Edna. "Why?" I said, or rather puffed out, in one enormous expiration, as I rounded the summit of yet another small hill. "You are eating all the hills like yam." "I haven't seen any hill yet," I replied, getting back some of my breath as I pedaled freely down the small, friendly descent that followed. These words were hardly out of my mouth when a stupid sheep and her four or five lambs rushed out of the roadside on my left. I braked sharply. Unfortunately Edna's back was resting on my left arm and prevented me applying the brake on that side effectively. So only the brake on the front wheel performed fully. The bicycle pitched forward and crashed on the road. Edna was thrown farther up the road and as soon as I got up, I rushed to help her to her feet again. Then I turned to gaze at the food in the sandy road. I could have wept. I just stood looking at it and biting my lip. Then Edna burst into nervous laughter which completed my humiliation. I didn't want to look at her. Without taking my eyes from the food I murmured that I was very sorry.

单选题Prevention is always preferable to a cure, and while much of the data are still preliminary, a growing body of evidence suggests【C1】______Ihe local green market may be a rich source of anticancer agents.【C2】______certain fruits and vegetables seem to have powerful tumor-fighting properties that researchers are【C3】______beginning to appreciate—and to study. A sampling of the current crop of findings: Scientists have long known that men who eat cooked tomato products such as pasta sauces【C4】______to have lower rates of prostate cancer. Until last week, however, the data were anything【C5】______conclusive. A study reported at last week"s meeting of the American Association for Cancer Research shows that daily doses of lycopene, an antioxidant that【C6】______tomatoes and gives them their red color, may not only prevent prostate cancer but【C7】______existing tumors as well. Previous studies showed that women who eat soy products【C8】______tofu and soy milk are less likely to develop breast cancer. But it was never clear why. Now a small study of two dozen women may point to an answer: soy seems to keep circulating levels of estrogen low,【C9】______inhibits breast cells【C10】______proliferating.

单选题Among all the malignancies, lung cancer is the biggest killer; more than 100, 000 Americans die of the disease. Giving up smoking is one of obvious ways to reduce the risk, but another answer may lie in the kitchen. According to a new report, even heavy smokers may be protected from developing lung cancer by eating a daily portion of carrots, spinach or any other vegetable or fruit containing a form of vitamin A called carotene. The finding, published in THE LANCET, is part of a long-range investigation of diet and disease. Since 1957, some American researchers have monitored the dietary habits and medical histories of 2, 000 middle-aged men employed by the Western Electric Co. in Chicago. Led by Dr. Richard Shekelle of St. Luke's Medical Center, the researchers recently began to sort out the links between the subjects' dietary patterns and cancer. Other studies of animals and humans have suggested that vitamin A offer some protection against lung cancer. The correlation seemed logical, explains Shekelle, since vitamin A is essential for the growth of the epithelial tissue that lines the airways of the lungs. Vegetables: But the earlier research did not distinguish between the two different forms of the vitamin. "Preformed" vitamin A, known as retinols found mainly in liver and dairy products like milk, cheese, butter and eggs. But vitamin A is also made in the body from carotene, which is abundant in a variety of vegetables and fruits, including carrots, spinach, squash, tomatoes, sweet potatoes and apples. In the study, Shekelle and his colleagues found little correlation between the incidence of lung cancer and the consumption of foods containing preformed vitamin A. But when they examined the data on carotene intake, they discovered a significant relationship. Among the 488 men who had the lowest level of carotene consumption, there were 14 cases of lung cancer; in a group of the same size that ate the most carotene, only two cases developed. The apparent protective effect of carotene held up even for long-time smokers—but to a lesser degree. Further studies will be necessary before the link between lung cancer and carotene can be firmly established. In the meantime, researchers warn against taking large numbers of vitamin A pills, because the tablets contain a form of the chemical that can be extremely toxic in high doses. Instead, they advise a well-balanced diet that includes goods rich in carotene. For a smoker, a half-cup of carrots every day might possibly make the difference between life and death.

单选题Personalized genetic diagnosis and therapy say you" re young and healthy, and you go in for a routine physical. Your doctor takes a blood sample and has it shipped to a lab. There, a medical technologist places your serum sample on a glass chip the size of a postage stamp. That gene chip might contain up to 50,000 microscopic spots—each with one of the genes in the human genome. When the doctor calls you with the results, he" 11 tell you which of thousands of human diseases you " re at risk for. If you have a defective gene that" s placing you at risk for disease, he might treat you with a healthy version of the gene to make up for it, keeping you out of harm" s way. Soon, such diagnoses and treatments could be routine, says Mark Kay, MD, a professor of genetics at Stanford University School of Medicine and president of the American Society of Gene Therapy. "In five years, you may be able to go to referral centers and get gene therapy," he says. Although gene therapists have talked like that for a while, and the field has tremendous promise, so far they have demonstrably cured humans of just one disease; severe combined immunodeficiency(SCID). Known as the bubble-boy disease, it decimates the immune system and causes children to die young from infections. While the treatment looks promising, the virus used to deliver the gene in one trial may have activated a gene that causes cancer. Such safety issues have dogged gene therapy. But gene therapists are pressing on. More than a dozen advanced clinical trials are underway that use genes to treat a variety of cancers, and other trials are ongoing for multiple sclerosis, AIDS and cystic fibrosis. Dr. Losordo has also begun a large trial of a gene therapy that seems to help patients regrow blood vessels that supply the heart— "grow your own bypass, if you will," he says. "It" s a very exciting time. " The best gene therapies just treat symptoms. The cells and tissues that make up our body still age, decay and die. "We know of no intervention that will slow, stop or reverse the aging process in humans," says Leonard Hayflick, PhD, professor of anatomy at the University of California, San Francisco, School of Medicine. Also, lifesaving technologies and treatments don" t come cheap, and sometimes terrible side effects emerge. "We will face some very difficult choices," says Thomas Murray, PhD, president of the Hastings Center in Garrison, New York, a think tank that explores ethical issues in biotechnology and health care. Fair enough. But perhaps it" s OK, for now, to step back and marvel at just how far we" ve come.

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Optical illusions are like magic, thrilling us because of their capacity to reveal the fallibility of our senses. But there's more to them than that, according to Dr. Beau Lotto, who is wowing the scientific world with work that crosses the boundaries of art, neurology, natural history and philosophy. What they reveal, he says, is that the whole world is the creation of our brain. What we see, what we hear, feel and what we think we know is not a photographic reflection of the world, but an instantaneous unthinking calculation as to what is the most useful way of seeing the world. It's a best guess based on the past experience of the individual, a long evolutionary past that has shaped the structure of our brains. The world is literally shaped by our pasts. Dr. Lotto, 40, an American who is a reader in neuroscience at University College London, has set out to prove it in stunning visual illusions, sculptures and installations, which have been included in art-science exhibitions. He explains his complex ideas from the starting point of visual illusions, which far from revealing how fragile our senses are show how remarkably robust they are at providing a picture of the world that serves a purpose to us. For centuries, artists and scientists have noted that a grey dot looks lighter against a dark background than being against a light background. The conventional belief was that it was because of some way the brain and eye is intrinsically wired. But Dr. Lotto believes it's a learnt response; in other words, we see the world not as it is but as it is useful to us. "Context is everything, because our brains have evolved to constantly re-define normality, " says Dr. Lotto. "What we see is defined by our own experiences of the past, but also by what the human race has experienced through its history, " This is illustrated by the fact that different cultures and communities have different viewpoints of the world, conditioned over generations. For example, Japanese people have a famous inability to distinguish between the "R" and the "L" sound. This arises because in Japanese the sounds are totally interchangeable. "Differentiating between them has never been useful, so the brain has never learnt to do it. It's not just that Japanese people find it hard to tell the difference. They literally cannot hear the difference. " Dr. Lotto's experiments are grounding more and more hypotheses in hard science. "Yes, my work is idea-driven, " he says. "But lots of research, such as MRI brain scanning, is technique-driven. I don't believe you can understand the brain by taking it out of its natural environment and looking at it in a laboratory. You have to look at what it evolved to do, and look at it in relationship to its ecology. "

单选题School authorities often refuse to face the problems; government drug-abuse agencies have done all too little to inform the public about it; many physicians still seem unaware of it when they examine teenagers. As a result, parents may still be the last to know that their children have fallen victim to the drug epidemic that has been raging for more than a decade among American's youth. In a 1980 survey of a middle income Cincinnati suburb, 38 percent of the sixth grade and 89 percent of the senior class said they used drugs and/or alcohol; 48% percent of the parents thought their children used alcohol, but only 8 percent thought their children used drugs. Fortunately, there is a few force at work against this epidemic — a nationwide movement of more than 400 parent groups formed to expose and battle drug use among teenagers and preteens. The groups, ranging in size from 15 members to more than 800, have different approaches and widely varying rates of success. Yet this parental crusade is the only major force in the country to have taken active, organized and effective steps aimed at stopping marijuana use. Why the concentration on marijuana? Because it is the illegal drug most used by kids. According to the 1982 National High School Senior Survey, 44 percent of U. S. high-school seniors had smoked pot during the year, and one out of seven of these were daily or near daily smokers. Moreover, in 1982, sociologists Richard Clayton and Harwin Voss reported a close-related connection between pot smoking and subsequent use of cocaine and heroin by young men. Of those, who had smoked pot fewer than 100 times, seven percent had graduated to cocaine, four percent to heroine. But of those who had smoked pot at least 1, 000 times, the equivalent of once a day for those years, 73 percent had gone on to cocaine, and one out of three had graduated to heroin. (Although heroin use among high-school seniors is minimal—0. 6 percent in the past year—multi-drug use is "in". ) Parent groups have found that by stopping their kids from smoking pot, they almost automatically stop all other illegal drugs, and cut down on alcohol use as well. The High School Senior Survey's statistics show that heavy pot smokers tend to be heavy drinkers, while those who do not use pot tend not to drink heavily. Since virtually all over the country teenage "partying" has come to mean "getting smashed and getting stoned" — on anything from pot to pills to hashish, ISD, angel dust and alcohol — some parent groups home in on the partying aspect. Parents Who Care (PWC) was started in November 1979 by 15 Palo Alto, Calif. , parents who were upset by stories of serious drug problems at parties. They held talk sessions with their children and learned, as founder Joann Lundgren observed, that most of them had never been to a party where the main activity was not getting high. The parents' solution: workshops showing kids how to give successful drug-and-alcohol-free parties. Says Margret Ranch, PWC director, "We've seen a change in attitude. Young people are feeling more comfortable saying no. "

单选题Here"s yet another to lose weight. Heavier people are more likely to be killed or seriously injured in car accidents than lighter people. That could mean car designers will have to build in new safety features to compensate for the extra hazards facing overweight passengers. In the US, car manufacturers have already had to redesign air bags so they inflate to lower pressures making them less of a danger to smaller women and children. But no one yet knows what it is that puts overweight passengers at extra risk. A study carried out in Seattle, Washington, looked at more than 26,000 people who had been involved in car crashes, and found that heavier people were at far more risk. People weighing between 100 and 119 kilograms are almost two-and-a-half times as likely to die in a crash as people weighing less than 60 kilograms. And importantly, the same trend held up when the researchers looked at body mass index(BMI)— a measure that takes height as well as weight into account. Someone 1.8 meters tall weighing 126 kilograms would have a BMI of 39, but so would a person 1.5 meters tall weighing 88 kilograms. People are said to be obese if their BMI is 30 or over. The study found that people with a BMI of 35 to 39 are over twice as likely to die in a crash compared with people with BMIs of about 20. It"s not just total weight, but obesity that"s dangerous. While they do not yet know why this is the case, the evidence is worth pursuing, says Charles Mock, a surgeon and epidemiologist at the Harborview Injury Prevention and Research Center in Seattle, who led the research team. He thinks one answer may be for safety authorities to use — heavier crash-test dummies when certifying cars are safe to drive. Crash tests normally use dummies that represent standard-sized males weighing about 78 kilograms. Recently, smaller crash-test dummies have also been used to represent children inside crashing cars. But larger and heavier dummies aren"t used, the US National Highway Traffic Safety Administration in Washington, D.C. told New Scientist. The reasons for the higher injury and death rates are far from clear. Mock speculates that car interiors might not be suitably designed for heavy people. Or obese people, with health problems such as high blood pressure or diabetes, could be finding it tougher to recover from injury.

单选题Women's minds work differently from men's. At least, that is what most men are convinced of. Psychologists view the subject either as a matter of frustration or a joke. Now the biologists have moved into this minefield, and some of them have found that there are real differences between the brains of men and women. But being different, they point out hurriedly, is not the same as being better or worse. There is, however, a definite structural variation between the male and female brain. The difference is in a part of the brain that is used in the most complex intellectual processes — the link between the two halves of the brain. The two halves are linked by a trunk line of between 200 and 300 million nerves, the corpus callosum (胼胝体) . Scientists have found quite recently that the corpus callosum in women is always larger and probably richer in nerve fibers than it is in men. This is the first time that a structural difference has been found between the brains of women and men and it must have some significance. The question is "What?", and, if this difference exists, are there others? Research shows that present-day women think differently and behave differently from men. Are some of these differences biological and inborn, a result of evolution? We tend to think that is the influence of society that produces these differences. But could we be wrong? Research showed that these two halves of the brain had different functions, and that the corpus callosum enabled them to work together. For most people, the left half is used for word-handing, analytical and logical activities; the right half works on pictures, patterns and forms. We need both halves working together. And the better the connections, the more harmoniously the two halves work. And, according to research findings, women have the better connections. But it isn't all that easy to explain the actual differences between skills of men and women on this basis. In schools throughout the world girls tend to be better than boys at "language subjects" and boys better at maths and physics. If these differences correspond with the differences in the hemispheric trunk line, there is an unalterable distinction between the sexes. We shan't know for a while, partly because we don't know of any precise relationship between abilities in school subject and the functioning of the two halves of the brain, and we cannot understand how the two halves interact via the corpus callosum. But this striking difference must have some effect and, because the difference is in the parts of the brain involved in intellect, we should be looking for differences in intellectual processing.