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| 发布时间：2006-8-14 15:27:49 | 信息来源：本站原创 | 浏览： | |
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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 ( 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 North-eastern 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 (生态系统 ) respond rapidly to reductions in atmospheric pollution, but that these findings should not be used as a license to pollute.
26. The study published in the journal Nature indicates that
A) lead deposits in arctic snow are on the increase
B) the Clean Air Act has not produced the desired results
C) the US is the major source of lead pollution in arctic snow
D) lead will stay in soil and snow longer than expected
27. Lead accumulation worldwide decreased significantly after the use of unleaded gas in the US
A) was introduced
B) was discouraged
C) was prohibited by law
D) was enforced by law
28. 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 studying the chemical elements of soil and snow in Northeastern America.
C) By comparing the chemical compositions of leaded gasoline used in various countries.
D) By observing the lead accumulations in different parts of the arctic area.
29. The authors of the Ambio study have found that
A) forests get rid of lead pollution faster than expected
B) lead deposits are widely distributed in the forests of the US
C) lead accumulations in forests are more difficult to deal with
D) the upper layers of soil in forests are easily polluted by lead emissions
30. It can be inferred from the last paragraph that scientists
A) lack sufficient means to combat lead pollution
B) still consider lead pollution a problem
Part III Vocabulary (20 minutes)
Directions: There are 30 incomplete sentences in this part. For each sentence there are four choices marked A), B), C) and D). Choose the ONE answer that best completes the sentence. Then mark the corresponding letter on the Answer Sheet with a single line through the centre.
31. Salaries for positions seem to be higher than for permanent ones.
A) temporary
B) voluntary
C) optional |
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