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  3. Lead deposits, which accumulated in soil and snow during the 1960’s and 70’s, were primarily the result of leaded gasoline emiss

Lead deposits, which accumulated in soil and snow during the 1960’s and 70’s, were primarily the result of leaded gasoline emiss

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问题      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.
The study published in the journal Nature indicates that
选项 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.
答案D
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。  
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