【正文】 nce the introduction of unleaded gasoline. Many scientists had believed that the lead would stay in soil and snow for a longer period. The authors of the Ambio study examined samples of the upper layers of soil taken from the same sites of 30 forest floors in New England, New York and Pennsylvania in 1980 and in 1990. The forest environment processed and redistributed the lead faster than the scientists had expected. Scientists say both studies demonstrate that certain parts of the ecosystem (生態(tài)系統(tǒng) ) re spond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute. 21. The study published in the journal Nature indicates that A) the Clean Air Act has not produced the desired results B) lead deposits in arctic snow are on the increase C) lead will stay in soil and snow longer than expected D) the US is the major source of lead pollution in arctic snow 22. Lead accumulation worldwide decreased significantly after the use of unleaded gas in the US A) was discouraged B) was enforced by law C) was prohibited by law D) was introduced 23. How did scientists discover the source of lead pollution in Greenland? A) By analyzing the data published in journals like Nature and Ambio. B) By observing the lead accumulations in different parts of the arctic area. C) By studying the chemical elements of soil and snow in Northeastern America. D) By paring the chemical positions of leaded gasoline used in various countries. 24. The authors of the Ambio study have found that A) forests get rid of lead pollution faster than expected B) lead accumulations in forests are more difficult to deal with C) lead deposits are widely distributed in the forests of the US D) the upper layers of soil in forests are easily polluted by lead emissions 25. It can be inferred from the last paragraph that scientists A) are puzzled by the mystery of forest pollution B) feel relieved by the use of unleaded gasoline C) still consider lead pollution a problem D) lack sufficient means to bat lead pollution Passage Four Questions 26 to 30 are based on the following passage. Exercise is one of the few factors with a positive role in longterm maintenance of body , that message has not gotten through to the average American, who would rather try switching to light beer and lowcalorie bread than increase physical exertion. The Centers for Disease Control, for example, found that fewer than onefourth of overweight adults who were trying to shed pounds said they were bining exercise with their diet. In rejecting exercise, some people may be discouraged too much by caloricexpenditure charts。s knowledge 20. Why do some Japanese parents send their children to university:based kindergartens? A) They can do better in their future studies. B) They can accumulate more group experience there. C) They can be individually oriented when they grow up. D) They can have better chances of getting a firstrate education. Passage Three Questions 21 to 25 are based on the following passage. Lead deposits, which accumulated in soil and snow during the 196039。s creativity C) lighten children39。s character 19. Free play has been introduced in some Japanese kindergartens in order to A) broaden children39。s artistic interests C) tapping children39。s higher education is superior to theirs 17. Most Americans surveyed believe that preschools should also attach importance to A) problem solving B) group experience believe that preschools should also attach importance to C) parental guidance D) individuallyoriented development 18. In Japan39。s chances of eventually being admitted to toprated schools and universities. Several more progressive programs have introduced free play as a way out for the heavy intellectualizing in some Japanese kindergartens. 16. We learn from the first paragraph that many Americans believe A) Japanese parents are more involved in preschool education than American parents B) Japan39。most Japanese preschools, surprisingly little emphasis is put on academic instruction. In one investigation, 300 Japanese and 210 American preschool teachers, child development specialists, and parents were asked about various aspects of early childhood education. Only 2 percent of the Japanese respondents (答問(wèn)卷者 )listed to give children a good start39。s because the prescription drugs available for the flu need to be taken soon after the illness sets in. As for colds, the sooner aperson starts taking overthecounter remedy, the sooner relief will e. The mon cold and the flu are both caused by viruses. More than 200 viruses can cause cold symptoms, while the flu is caused by three viruses flu A, B and C. There is no cure for eitherillness, but the flu can be prevented by the flu vaccine ( ~~ ), which is, for most people, the bestway to fight the flu, according to the ALA. But if the flu does strike, quick action can help. Although the flu and mon cold have manysimilarities, there are some obvious signs to look for. Cold symptoms such as stuffy nose, runny nose and scratchy throat typically develop gradu ally, and adults and teens often do not get a fever. On the other hand, fever is one of the character istic features of the flu for all ages. And in general, flu symptoms including fever and chills, sore throat and body aches e on suddenly and are more severe than cold symptoms. The ALA notes that it may be particularly difficult to tell when infants and preschool age ch