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 actually 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 of manufacturing(制造业) 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 fossil fuels (coal and oil) is creating a “greenhouse effect” — hold in heat reflected from the earth and 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 cap(极区冰层) 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 blocking sunlight and lowering the earth’s temperature — a result that would be equally disastrous(引起灾难的). 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 report concluded that the greenhouse effect is very possible). Perhaps, if we are lucky enough, the two tendencies will offset (相互抵消) each other and the world’s temperature will stay about the same as it is now. Driven by economic profits, people pay less attention to 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 worthwhile?
43. As pointed out at the beginning of the passage, people used to think that air pollution _______.
A. had a damaging effect on health
B. caused widespread damage in the countryside
C. affected the entire eastern half of the United States
D. existed only in urban and industries areas
44. As to the greenhouse effect, the author __________.
A. is uncertain of its cause B. refuse to admit as a problem
C. share the same view with the scientist D. thinks that it will destroy the world soon
45. It can be concluded that ____________.
A. temperature almost hasn’t changed over the past decade.
B. the world’s temperature will remain the same in the years to come.
C. raising the world’s temperature only a few degrees would not do much harm to life on earth.
D. lowering the world’s temperature only a few degrees would lead to disaster to farming .
46. This passage is mainly about __________.
A. the greenhouse effect B. the burning of fossil fuels
C. the potential effect of air pollution D. the likelihood of a new ice age