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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 authors of the Ambio study have found that
选项 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.
答案A
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。  
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