Air PollutionThere was one thought that air pollution affected only th

AirPollution

Therewasonethoughtthatairpollutionaffectedonlytheareasimmediatelyaroundlargecitieswithfactoriesandheavyautomobiletr affic.____1____

Onseveraloccasionsoverthepastd ecade,aheavycloudofairpollutionhascoveredtheeastoftheUnitedStatesandbroughthealthwarningsinruralareasawayfromanymajorconcentr ationofmanufacturingandautomobiletr affic.Infact,theveryclimateoftheentireearthmaybeinfectedbyairpollution

Somescientistsconsiderthattheincreasingconcentr ationofcarbondioxide((二氧化碳)intheairresultingfromtheburningofcoalandoiliscreatinga"greenhouseeffect".Itconservesheatr eflectedfromtheearthandraisedtheworld’saveragetemperature.___2___ThusmuchofthepolaricecapwillmeltandcitiessuchasNewYork,Boston,Miami,andNewOrleanswillbeinwater.

___3___Thisisaresultthatwouldbeequallydisastr ous.Adropofjustafewdegreescouldcreatesomethingclosebetoanewiceage,andwouldmakeagriculturedifficultorimpossibleinmanyofourtopfarmingareas.

Todaywedonotknowforsurethateitheroftheseconditionswillhappen.___4___Drivenbyeconomicprofit,peopleneglectbythedamageonourenvironmentcausedbythe"advancedcivilization".___5___Butisitr eallyworthwhile?

Perhaps,ifweareluckyenough,thetwotendencieswilloffset(抵消)eachotherandtheworld'stemperaturewillstayaboutthesameasitisnow.

Ifthisviewiscorrect,theworld'stemperatureisraisedonlyafewdegrees.

Maybetheairpollutionisthepricethehumanbeingshavetopayfortheirdevelopment

Atpresent,werealizethatalthoughthesearetheareaswiththeworstairpollution,theproblemisliterallyworldwide

Lately,globalwarmingisbecomingaseriousproblem

Anotherview,lesswidelyheld,isthatincreasingparticularmatterintheatmosphere(大气)isblockingsunlightandloweringtheearth'stemperature.

答案及解析：​​​​​​​第三段论述了一些科学家对温室效应的看法,阐述了温室效应产生的原因及其后果。该空格位于段落中间,因此空格处的内容也应与温室效应及地球温度上升有关,而不应是其他的新信息。因此只有选项B“…theworld'stemperatureisraisedonlyafewdegrees"在语义上符合题意。