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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.
It can be inferred from the last paragraph that scientists
选项 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.
答案C
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。  
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