单选题 Passage 1
Lead deposits, which accumulated in soil and snow during the 1960's and 70's, were primarily the result of leaded gasoline emissions originating in the United States. In the twenty years that the Clean Air Act has mandated unleaded gas use in the United States, the lead accumulation worldwide has decreased significantly.
A study published recently in the journal Nature shows that air-borne leaded gas emissions from the United States were the leading contributor to the high concentration of lead in the snow in Greenland. The new study is a result of the continued research led by Dr. Charles Boutron, an expert on the impact of heavy metals on the environment at the National Center for Scientific Research in France. A study by Dr. Boutron published in 1991 showed that lead levels in arctic (北极的) snow were declining.
In his new study, Dr. Boutron found the ratios of the different forms of lead in the leaded gasoline used in the United States were different from the ratios of European, Asian and Canadian gasolines and thus enabled scientists to differentiate the lead sources. The dominant lead ratio found in Greenland snow matched that found ingasoline from the United States.
In a study published in the journal Ambio, scientists found that levels in soil in the Northeastern United States had decreased markedly since 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 respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.

单选题 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 on the increase.
C. lead will stay in soil and snow longer than expected.
D. the U.S. is the major source of lead pollution in arctic snow.

【正确答案】 D

【答案解析】细节题。根据原文第二段第一句：最近，在科学期刊《自然》杂志上发表的一篇研究文章指出，空气中的含铅废气是造成格陵兰岛的雪中含铅量高的主要原因，这些废气都是美国排放的。leading contributor所指的就是来自美国的废气，因此美国便是格陵兰岛污染的“罪魁祸首”，可以得出D项答案。从后文可知，洁净条例对抑制、降低铅污染起到了至关重要的作用，所以A违背原意；Charles Boutron博士1991年发布的一项研究显示，北极雪中的铅含量正在逐年减少，所以B违背原意；从文中第五段可知，科学家们曾经以为，铅会在soil和snow中长时间滞留，文中还指出，铅在土壤中滞留的研究是发表在期刊Ambio上的，所以C违背原意。

单选题 Lead accumulation worldwide decreased significantly after the use of unleaded gas in the U.S.
A. was discouraged. B. was enforced by law.
C. was prohibited by law. D. was introduced.

【正确答案】 B

【答案解析】细节题。根据第一段末句：自从美国实行空气洁净条例后，20年间，全世界的铅沉积水平都大大降低。理解mandate的意思“强制执行”，同义转述，即实行空气洁净条例是立法通过的，所以B正确。无铅汽油的使用是被提倡的，所以A违背原意；无铅汽油的使用是被立法通过，而不是禁止使用，所以C违背原意；D不够具体明确，应该是通过立法的途径，而不单单是简单的引入。

单选题 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 comparing the chemical compositions of leaded gasoline used in various countries.

【正确答案】 D

【答案解析】细节题。根据原文第三段第一句“…the ratios of the different forms of lead in the leaded gasolines…”可知，不同国家和地区的汽油中铅的含量不同；根据“…thus enabled scientists to differentiate the lead sources．”可知，专家可以通过汽油中的铅含量来判断此种铅来自于何地。显然，就是利用这种判断汽油中铅含量的方法得出格陵兰岛的铅污染主要来自美国的结论。所以D正确。原文中没有提到要分析Nature和Ambio中报告给出的数据，所以A不对；原文没有提及观察北极不同区域铅的累积情况，所以B不对；对美国东北部土质进行监测的目的是测量土壤中铅的含量，见第四段“…that lead levels in soil…decreased markedly since…”，说明C也不对。

单选题 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 U.S..
D. the upper layers of soil in forests are easily polluted by lead emissions.

【正确答案】 A

【答案解析】细节题。根据原文倒数第二段“The forest environment processed and redistributed the lead faster than the scientists had expected．”森林处理和重新分配铅污染的能力超出科学家的预料，同义转述是森林去除、净化铅污染的能力比科学家预计得要强，可知A正确。森林中的铅积累好处理，说明B与文中所述相反。原文没有提及铅沉积在美国的森林中广泛分布，所以C不对；文中没有提到哪层土壤更容易被污染，所以D也不对。

单选题 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 combat lead pollution.

【正确答案】 C

【答案解析】推论题。根据最后一段：尽管生态系统的某些环节对空气污染的改善反应迅速(respond rapidly to reductions in atmospheric pollution,…)，但这些研究成果不应该被当作对环境污染的许可。这说明，铅污染仍然应被重视，所以C正确。文中没有提到科学家们被森林污染所困扰，所以A不对；文中虽然举出了使用无铅汽油后，铅污染减少，但并没有说铅污染已经解决，而且，“…these findings should not be used as a license to pollute.”，即暗指铅污染仍然应被重视，科学家们还能“feel relieved”，所以B不对；文中没有提到和污染斗争的方法手段问题，所以D也不对。