阅读理解。
It was once thought that air pollution affected only the area immediately around large cities with factories
and/or heavy automobile traffic. Today, we know 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 entire eastern half of the United States and led to health warnings even in rural areas away from
any major concentration of manufacturing and automobile traffic. In fact, the very climate of the entire earth
may be affected by air pollution. Some scientists feel 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"-holding 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 will melt and cities such as New York,
Boston, Miami, and New Orleans will be under water.
Another view, less widely held, is that increasing particulate (废气排往空中而形成的微粒、颗粒) matter
in the atmosphere is blocking 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 new ice age and would make
agriculture difficult or impossible in many of our top farming areas. At present we do not know for sure that
either of these conditions will happen (though one recent government report prepared by experts in the field
concluded that the greenhouse effect is very likely). Perhaps, if we are very lucky, the two tendencies will
offset each other and the world's temperature will stay about the same as it is now.
1. 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 damaging effects on health
D. existed merely in urban and industrial areas
2. As far as the greenhouse effect is concerned, the author _____.
A. shares the same view with the scientists
B. is uncertain of its occurrence
C. rejects it as being ungrounded
D. thinks that it will destroy the world soon
3. The underlined word "offset" in Para. 2 could best be replaced by _____.
A. slip into
B. make up for
C. set up
D. catch up with
4. This passage is mainly concerned with _____.
A. the greenhouse effect
B. the burning of fossil fuels
C. the potential effect of air pollution
D. the likelihood (可能性) of a new ice age
