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XX年12月英语四级考试(仔细阅读)xx年12月英语四级考试(仔细阅读)
56、Questions56-61are basedon thefollowing passage. It wasonce thoughtthat air pollution affectedonly thearea immediatelyaround largecities withfactories andheavy automobile traffic.Today,we knowthat althoughthese arethe areaswith theworst airpollution,the problemis literallyworldwide.On severaloasions overthe pastdecade,a heavycloud ofairpollutionhas coveredthe entireeastern halfof theUnited Statesand ledto healthwarnings even inrural areasaway fromany majorconcentration ofmanufacturing andautomobiletraffic.In fact,the veryclimate ofthe entireearth maybe affectedby airpollution. Some scientistsfeel thatthe increasingconcentration ofcarbon dioxidein theair resultingfrom theburning offossil fuelscoaland oil.is creatinga“greenhouse effect”一holding inheat reflectedfrom theearth andraising the world’s averagetemperature.If thisview iscorrect andtheworld’s temperatureis raisedo...。