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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.
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 推理题。本题是段内推理题。最后一段的大意是：科学家们说，这两项研究表明，当人气污染状况减轻时，生态系统的某些部分很快就能感受到。但同时表明，这些研究结果不应成为我们污染环境的理由。选项A)与这一段的意思不符，选项B)只是前一句话产生的结果，忽视了更重要的后一句话的内容，也不对。选项D)，原文没有提及，当然可以排除。所以选项C)是对后一句话最好的解读。
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