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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 airborne 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 gasoline and thus enable scientists to differentiate (分区) the lead sources. The dominant lead ratio found in Greenland snow matched that found in gasoline from the United States.
    In a study published in the journal Ambio, scientists found that lead 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 up per 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(生态系统) respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.
How did scientists discover the source of lead pollution in Green land?
选项 A、By analyzing the data published in journals like Nature and Ambio.
B、By observing the lead accumulation in different parts of the arctic area.
C、By studying the chemical elements of soil and snow in North eastern America.
D、By comparing the chemical compositions of leaded gasoline used in various countries.
答案D
解析 细节判断题。本题答案可在第三段找到。这段话大意是：有位博士发现，美国含铅汽油中不同结构铅元素(即不同的铅化合物)的比率与欧洲、亚洲和加拿大的不同，这使得科学家们能够区分铅的来源地。而格陵兰岛积雪中发现的不同结构铅的比率与美国汽油中所含的不同结构铅的比率相吻合。从中可以看出，选项D)“通过比较不同国家使用的含铅汽油中的化学成分”应当是恰当的归纳。
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