华
U2:Lead deposits, which accumulated in soil and snow during the 1960s and 1970s, were primarily the result of leaded gasoline emissions originating in the United States. 21. The study published in the journal Nature indicates that _______. A. the Clean Air Act has not produced the desired results B. lead deposits in Arctic snow are on the increase C. lead will stay in soil and snow longer than expected D. the US is the major source of lead pollution in Arctic snow 请根据需要填入 Script: 正确答案：D 得分：0 分22. Lead accumulation worldwide decreased significantly after the use of unleaded gas in the US _______. A. was discouraged B. was enforced by law C. was prohibited by law D. was introduced 正确答案：B 得分：2 分 23. How did scientists discover the source of lead pollution in Greenland? A. By analyzing the data published in journals like "Nature" and "Ambio". B. By observing the lead accumulations in different parts of the arctic area. C. By studying the chemical elements of soil and snow in Northeastern America. D. By comparing the chemical compositions of leaded gasoline used in various countries. 请根据需要填入 Script: 正确答案：D 得分：0 分 24
. The authors of the Ambio study have found that _______. 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 US D. the upper layers of soil in forests are easily polluted by lead emissions 请根据需要填入 Script: 正确答案：A 得分：0 分 25. It can be inferred from the last paragraph that scientists _______. 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 请根据需要填入 Script: 正确答案：C 得分：0 分