单选题The Greatest Mystery Of Whales The whale is a warm-blooded, air-breathing animal, giving birth to its young alive, sucking them—and, like all mammals, originated on land. There are many front flippers (鳍状肢), used for steering and stability, are traces of feet, 1 of this. Its immense strength is 2 into the great body of the big whales, and in fact most of a whale"s body is one gigantic muscle. The blue whale"s pulling strength has been estimated 3 400 horsepower. One specimen was reported to have towed (拖) a whaling vessel for seven hours at the 4 of eight knot (节). An angry whale will 5 . A famous example of this was the fate of Whaler Essex, 6 was sunk off the coast of South America early in the last century. More recently, steel ships have 7 their plates buckled (使弯曲) in the same way. Sperm whales (抹香鲸) were known to seize the old-time whaleboats in their jaws and crush them. The greatest 8 of whales is their diving ability. The sperm whale dives to the bottom for his 9 food, the octopus (章鱼). In that search he is known to go as far down as 3,200 feet, where the 10 is 1,400 pounds, to a square inch. Doing so he will 11 underwater long as one hour. Two special skills are involved in this storing up enough 12 (all whales are air-breathed) and tolerating the great change in pressure. Just how he does it scientists have not 13 . It is believed that some of the oxygen is stored in a special 14 of blood vessels, rather than just held in the lungs. And it is believed that a special kind of oil in his head is some sort of compensating mechanism that 15 adjusts the internal pressure of his body. But since you can"t bring a live whale into the laboratory for study, no one knows just how these things work.

单选题They didn't seem to appreciate the {{U}}magnitude{{/U}} of the problem. A. existence B. importance C. cause D. situation

单选题You must shine your shoes.

单选题The American Family In the American family the husband and wife usually share important decision making. When the children are (51) enough, they take part as well. Foreigners are often surprised by the permissiveness (宽容) of American parents. The old rule that "children should be seen and not heard" is rarely (52) , and children are often allowed to do (53) they wish without strict control of their parents. The father seldom expects his children to listen to him (54) question, and children are encouraged to be (55) at an early age. Some people believe that American parents carry this freedom (56) far. Others think that a strong father image, would not (57) the American values of equality and independence. Because Americans emphasize the importance of independence, young people are expected to (58) their parental families by the time they have (59) their late teens or early twenties. Indeed, not to do so is often regarded as a (60) , a kind of weak dependence. This pattern of independence often results in serious (61) for the aging parents of a small family. The average American is expected to live (62) the age of 70. The job-retirement age is (63) 65. The children have left home, married, and (64) their own households. At least 20 percent of all people over 65 do not have enough retirement incomes. (65) the major problem of many elderly couples is not economic. They feel useless and lonely with neither an occupation nor a close family group.

单选题An expert in any field may be defined as a person who possesses specialized skills and is capable of {{U}}rendering{{/U}} very competent services.

单选题As a result, it is proved to be foolish.A. lovelyB. stupidC. practicalD. useful

单选题New Product Will Save Lives Drinking water that looks clean may still contain bugs (虫子), which can cause illness. A small company called Genera Technologies has produced a testing method in three stages, which shows whether water is safe. The new test shows if water needs chemicals added to it, to destroy anything harmful. It was invented by scientist Dr. Adrian Patton, who started Genera five years ago. He and his employees have developed the test together with a British water company. Andy Headland, Genera"s marketing director, recently presented the test at a conference in the USA and forecast good American sales for it. Genera has already sold 11 of its tests at $ 42,500 a time in the UK and has a further four on order. It expects to sell another 25 tests before the end of March. The company says it is the only test in the UK to be approved by the government. Genera was formed five years ago and until October last year had only five employees; it now employs 14. Mr. Headland believes that the company should make around $19 million by the end of the year in the UK alone.

单选题{{B}}第三篇{{/B}} {{B}}New Attempts to Eradicate AIDS Virus{{/B}} A high-profile attempt to eradicate the AIDS virus in a few patients continues to show promise. But researchers won't know for a year or more whether it will work, scientist David Ho told journalists this Wednesday for the Fourth Conference in Viruses and Infections. "This is a study that's in progress," says Ho, head of the Aaron Diamond AIDS Research Center, New York. The study involves 20 people who started combinations of anti-HIV drugs very early in the course of the disease, within 90 days of their infections. They've been treated for up to 18 months. Four others have dropped out because of side effects or problems complying with the exacting drug system. The drugs have knocked the AIDS virus down to undetectable levels in the blood of all remaining patients. And, in the latest development, scientists have now tested lymph nodes and semen from a few patients and found no virus reproducing there, Ho says. "Bear in mind that undetectable does not equal absent," Ho says. Ho has calculated that the drugs should be able to wipe out remaining viruses — at least from known reservoirs throughout the body — in two to three years. But the only way to prove eradication would be to stop the drugs and see if the virus comes back. On Wednesday,' Ho said he wouldn't ask any patient to consider that step before 2 years of treatment. And he emphasized that he is not urging widespread adoption of such early, aggressive treatment outside of trials. No one knows the long-term risks. But other scientists are looking at similar experiments. A federally funded study will put 300 patients on triple-drug treatments and then see if some responding well after six months can continue to suppress the virus on just one or two drugs, says researcher Douglas Richman of the University of California, San Diego. Some patients in that study also may be offered the chance to stop therapy after 18 months or more, he says.

单选题Why More Fertilizer Harms Plant Diversity The 35-year-old mystery of why fertilizers decrease biodiversity has finally been solved. The secret? They increase competition for sunlight. Adding fertilizers 1o grasslands increases the productivity of plants, but leads to a major drop in biodiversity. The amount of nitrogen(氮) and phosphorus(磷) available to plants has doubled in the last 50 years, but the reason why this has harmed diversity has not been easy to answer. The debate has centred on whether fertilizers increase competition above or below ground-for sunlight or soil resources? To resolve the argument, Yann Hautier and Andy Hector from the University of Zurich, Switzerland built their own experimental plant community from scratch. Hautier's team grew 32 plant communities for tour years, before transferring them to a glass house. Each community comprised four different sets of six species. Half were fertilized, the others were left unfertilized. Half of each of these sets had light added, using a system of three fluorescent tubes that were raised as the canopy grew, while the other half were left to grow in normal light conditions. After two years, the sets that were fertilized in normal light conditions showed a significant increase in productivity anti biomass, but lost around one-third of their species diversity compared to the unfertilized groups. Those that were fertilized and given additional light showed no significant loss of diversity. To uncover whether underground competition for root space had any influence on biodiversity, the team added two new species of plant at the beginning of the second year. The roots of half these plants were contained in plastic tubes, which prevented any below-ground competition: the other half were left exposed. Removing below, ground competition from fertilized plots had no detectable impact on the mortality (死亡率) of the seedlings (幼苗), compared to those that were exposed to full root competition, says Hautier. "In the fertilized groups without additional light, there was no difference with or without the root-tube-they died both ways. Even if we remove competition below ground, these plants are unable to grow. " Drew Purves, a computational ecologist from Microsoft Research Cambridge is impressed with the team's findings. "This is a rare example of a simple experiment providing an unambiguous answer to an important ecological question. If these results are general to temperate grasslands-which seems likely-then we can start to develop more targeted policies to offset (补偿, 抵消) one of the most important sources of diversity loss in grasslands. /

单选题The govemment has protected farmers from damaging drops in grain prices.A. slightB. surprisingC. suddenD. harmful

单选题Why are jade and jade finders mentioned in the passage?

单选题The value of a particular variety of clay for pottery is related to its mineralogical and chemical {{U}}makeup{{/U}}.

单选题This text is too difficult to comprehend. A. understand B. digest C. summarize D. read

单选题One of the Nobel Economics Prize winner once said: "Every leisure act has an economic Upayoff/U for someone."

单选题Almost all economists agree that nations {{U}}gain{{/U}} by trading with one another.

单选题The leader collaborate with you in the project.

单选题Sleep Lets Brain File Memories To sleep. Perchance to file? Findings published online this week by the "Proceedings of the National Academy of Sciences" further support the theory that the brain organizes and stows memories formed during the day while the rest of the body is catching zzz's. Gyorgy Buzsaki of Rutgers University and his colleagues analyzed the brain waves of sleeping rats and mice. Specifically, they examined the electrical activity emanating from the somatosensory neocortex (an area that processes sensory information) and the hippocampus, which is a center for learning and memory. The scientists found that oscillations in brain waves from the two regions appear to be intertwined. So-called sleep spindles (bursts of activity from the neocortex) were followed tens of milliseconds later by beats in the hippocampus known as ripples. The team posits that this interplay between the two brain regions is a key step in memory consolidation. A second study, also published online this week by the "Proceedings of the National Academy" of Sciences", links age-associated memory decline to high glucose levels. Previous research had shown that individuals with diabetes suffer from increased memory problems. In the new work, Antonio Convit of New York University School of Medicine and his collaborators studied 30 people whose average age was 69 to investigate whether sugar levels, which tend to increase with age, affect memory in healthy people as well. The scientists administered recall tests, brain scans and glucose tolerance tests, which measure how quickly sugar is absorbed from the blood by the body's tissues. Subjects with the poorest memory recollection, the team discovered, also displayed the poorest glucose tolerance. In addition, their brain scans showed more hippocampus shrinkage than those of subjects better able to absorb blood sugar. "Our study suggests that this impairment may contribute to the memory deficits that occur as people age." Convit says. "And it raises the intriguing possibility that improving glucose tolerance could reverse some age-associated problems in cognition." Exercise and weight control can help keep glucose levels in check, so there may be one more reason to go to the gym.