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 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 (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 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.

62. 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

63. Lead accumulation worldwide decreased significantly after the use of unleaded gas in the US ________.
A) was discouraged C) was prohibited by law
B) was enforced by law D) was introduced
64. 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.

65. 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

66. 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

Part V Cloze (15 minutes)
Directions: There are 20 blanks in the following passage. For each blank there are four choices marked A), B), C) and D) on the right side of the paper. You should choose the ONE that best fits into the passage. Then mark the corresponding letter on Answer Sheet 2 with a single line through the centre.

For the past two years, I have been working on students’ evaluation of classroom teaching. I have kept a record of informal conversations __67__ some 300 students from at __68__ twenty-one colleges and universities. The students were generally __69__ and direct in their comments __70__ how course work could be better __71__. Most of their remarks were kindly ___72___ — with tolerance rather than bitterness—and frequently were softened by the __73__ that the students were speaking __74__ some, not all, instructors. Nevertheless, __75__ the following suggestions and comments indicate, students feel __76__ with things-as-they-are in the classroom.
Professors should be __77__ from reading lecture notes. “It makes their __78__ monotonous（单调的）.”
If they are going to read, why not __79__ out copies of the lecture? Then we __80__ need to go to class. Professors should __81__ repeating in lectures material that is in the text-book. “__82__ we’ve read the material, we want to __83__ it or hear it elaborated on, __84__ repeated.” “A lot of students hate to buy a __85__ text that the professor has written __86__ to have his lectures repeat it.”
67. A) involving B) counting C) covering D) figuring
68. A) best B) least C) length D) large
69. A) reserved B) hard-working C) polite D) frank
70. A) over B) at C) on D) of
71. A) presented B) submitted C) described D) written
72. A) received B) addressed C) made D) taken
73. A) occasion B) truth C) case D) fact
74. A) on B) about C) at D) with
75. A) though B) whether C) as D) if
76. A) dissatisfied B) unsatisfactory C) satisfied D) satisfactory
77. A) interfered B) interrupted C) discouraged D) disturbed
78. A) voices B) sounds C) pronunciation D) gestures
79. A) hold B) leave C) drop D) give
80. A) couldn’t B) wouldn’t C) mustn’t D) shouldn’t
81. A) refuse B) prohibit C) prevent D) avoid
82. A) Once B) Until C) However D) Unless
83. A) remember B) argue C) discuss D) keep
84. A) yet B) not C) and D) or
85. A) desired B) revised C) required D) deserved
86. A) about B) how C) but D) only

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