阅读理解Itwasoncethoughtthatairpollution

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 countrysideB.affected the entire eastern half of the United StatesC.had damaging effects on healthD.existed merely in urban and industrial areas2.As far as the greenhouse effect is concerned, the author ______.A.shares the same view with the scientistsB.is uncertain of its occurrenceC.rejects it as being ungroundedD.thinks that it will destroy the world soon3.The underlined word “offset in Para. 2 could best be replaced by______.A.slip intoB.make up forC.set upD.catch up with4.This passage is mainly concerned with ______.A.the greenhouse effectB.the burning of fossil fuelsC.the potential effect of air pollutionD.the possibility of a new ice age

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