IfyouliveinacityinNorthAmericaorEurope, youhaveprobablyneverthoughtmuchaboutwater. Wheneveryouneedsome, youturnonthetapandthereitis. Millionsofpeopleinotherpartsoftheworldarenotsolucky. Theyhavetroublegettingenoughcleanwaterfortheirbasicneeds. Thissituationmaysoonbecomecommonallaroundtheworld, scientistsbelieve. Infact, theysaythatthelackofcleanwatermaybeoneofthebiggestissuesinthetwenty-firstcentury.
Thereasonsforthisareclear. Ontheonehand. peopleareusingmorewaterthaneverbefore. Overthelastfiftyyears, thepopulationoftheworldhasmorethandoubled. Ontheotherhand, manysourcesofsurfacewatersuchasrivers, lakes, andstreamsaretoopollutedandunhealthyforuseasdrinkingwater.
Thishasforcedmoreandmorepeopletodrillwellssotheycangetwaterformunderground. Thereareenormousamountsofwaterdeepundergroundinlakescalledaquifers. Untilrecently, scientistsbelievedthisundergroundwaterwassafefrompollution. Then, inthe 1980s. peopleintheUnitedStatesbegantofindchemicalsintheirwellwater, andscientiststookacloserlookatwhatwashappening. WeldonSpring, Missouri, forexample, wasthesiteofabombfactoryduringWorldWar Ⅱ. Thefactorywasdestroyedafterthewar. butpoisonouschemicalsremainedontheground. Veryslowly, thesechemicalsdrippeddownthroughthegroundandintotheaquifer. Oncetheydid, however, thewaterformthataquiferwasnolongerdrinkable.
【2013年6月英语六级考试备考深度阅读试题模拟与解析（9）】相关文章：
★ 2013年6月英语六级考试备考深度阅读试题模拟与解析（10）
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