2012高考英语精选备考题库系列(含详解)阅读理解(二)

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1、2012高考英语精选备考题库系列（含详解）阅读理解（二）备战2012高考，精选阅读200篇，适合高三上学期使用，希望对大家有帮助。（2011-8）Haveyouevernoticedthecolourofthewaterinariverorstreamafteraheavyrainfall?Whatdoyouthinkcausedthischangeincolour?Itissoilthathasbeenwashedintotheriverfromtheriverbankorfromthenearbyfields.Componentsof

2、SoilSoilismadeupofanumberoflayers(层),eachhavingitsowndistinctivecolourandtexture.Theupperlayerisknownasthelitter.Itactslikeablanket，limitingtemperaturechangesandreducingwaterloss.Thetopsoillayerismadeupofsmallparticlesofrockmixedwithrottenplantandanimalmattercalledhumus(腐

3、殖质),whichisblackandgivesthetopsoilitsdarkcolour.Thislayerisusuallyrichinnutrients,oxygen,andwater.Belowthetopsoilisthesubsoil,alayerthatcontainsmorestonesmixedwithonlysmallamountsoforganicmatter.Thislayerislighterincolourbecauseofthelackofhumus.Beneaththesoilliesalayerofb

4、edrock.Soilformsfromthebottomup.Overtimebedrockisattackedbyrain,wind,frost,andsnow.Itisgraduallybrokendownintosmallerparticlesinaprocesscalledweathering.Plantsbegintogrow，androttenmaterialsenrichthetopsoil.MostofthesoilinEasternCanada，forexample，wasformedfromweatheredrock

5、thatwasexposedwhentheicedisappeared12,000yearsago.WaterBeneaththeSoilSurfacewatercollectsandflowsabovethegroundinlakes，ponds,andrivers.Onceinthesoilorrock,itiscalledgroundwater.Gravitypullsgroundwaterthroughthesoilinaprocesscalledpercolation(渗透).Eventuallythewaterreachesa

6、layercalledthewatertable.Underthisisbedrockthroughwhichwatercannotpercolate.Aswaterpercolatesdownward,itdissolvesorganicmatterandmineralsfromthesoilandcarriesthemtodeeperlayers.Thiscausesaseriousproblembecauseplantsrequirethesenutrientsforgrowth.SoilpHSoilcanbeacidic,neut

7、ral,orbasic.ThepHofthesoilisdeterminedbythenatureoftherockfromwhichitwasformed，andbythenatureoftheplantsthatgrowandrotinit.TheacidityofrainandsnowcanlowerthepHofthegroundwaterthatentersthesoil.Byburningfossilfuelssuchascoal，oilandgasoline，humanshavebeencontributingtohighe

8、rlevelsofacidityinmanysoils.Whenfossilfuelsareburned，gasesarereleasedintotheairandthenfallbackto