E
There was one thought that air pollution affected only the area immediately around large cities with factories and heavy automobile traffic. At present, we realize that although these are the areas with the worst air pollution, the problem is worldwide. On several occasions over the past decade, a heavy cloud of air pollution has covered the east of the United States and brought health warnings in rural areas away from any major concentration （集中）of manufacturing and automobile traffic. In fact, the very climate of the entire earth may be infected by air pollution.
Some scientists consider that the increasing concentration of carbon dioxide in the air resulting from the burning of coal and oil is creating a “greenhouse effect” - raising the world’s average temperature. If this view is correct and the world’s temperature is raised only a few degrees, much of the polar ice will melt and cities such as New York, Boston, Miami, and New Orleans will be in water.
Another view, less widely held, is that increasing particular matter in the atmosphere is preventing sunlight and lowering the earth’s temperature - a result that would be equally disastrous. A drop of just a few degrees could create something close to a new ice age, and would make agriculture difficult or impossible in many of our top farming areas. Today we do not know for sure that either of these conditions will happen though one recent government reports that the greenhouse effect is very possible. Perhaps, if we are lucky enough, the two tendencies will offset（抵消）each other and the world’s temperature will stay about the same as it is now. Driven by economic profits, people don’t think about the damage on our environment caused by the “advanced civilization”. Maybe the air pollution is the price the human beings have to pay for their development. But is it really worth?
72. As pointed out at the beginning of the passage, people used to think that air pollution ________.
A. caused widespread damage in the countryside
B. affected the entire eastern half of the United States
C. had damaged effect on health
D. existed only in urban and industrial areas
73. As to the greenhouse effect, the author ________.
A. shares the same view with the scientists
B. is uncertain of its happening
C. rejects it as being ungrounded
D. thinks it will destroy the world soon
74. It can be concluded from the last paragraph that ________.
A. lowering the world’s temperature only a few degrees would lead major farming areas to disaster
B. raising the world’s temperature only a few degrees would not do much harm to life on earth
C. almost no temperature variations have occurred over the past decade
D. the world’s temperature will remain constant in the years to come
75. This passage is mainly about ________.
A. the greenhouse effect
B. the burning of coal and oil
C. the potential effect of air pollution
D. the likelihood of a new ice age

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