12月英语四级考试最新预测试卷(阅读)_大学英语阅读

12月英语四级考试最新预测试卷(阅读)

　　A) a social issue calling for immediate attention

　　B) not necessary among family members

　　C) a sign of social progress

　　D) not as simple as it seems

　　Passage Two

　　Questions 62 to 66 are based on the following passage.

　　Lead deposits, which accumulated in soil and snow during the 1960s and 70s, 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 world-wide 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 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 enabled scientists to differentiate the lead sources. The dominant lead ratio found in Greenland snow matched that found in gasoline from the United States.