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TOEFL全真试题阅读部分TOEFL全真试题阅读部分TOEFL全真试题（2-2）VOCABULARYANDREADINGCOMPREHENSIONQuestions1-13Atmosphericpressurecansupportacolumnofwaterupto10metershigh.Butplantscanmovewatermuchhigher,thesequoiatreecanpumpwatertoitsverytop,morethan100metersabovetheground.Untiltheendofthenineteenthcentury,themovementofwatersintreesandothertallsplantswasamystery. Somebotanistshypothesizedthatthelivingcellsofplantsactedaspumps,butmanyexperimentsdemonstratedthatthestemsofplantsinwhichallthecellsarekilledcanstillmovewatertoappreciableheights.Otherexplanationsforthemovementofwaterinplantshavebeenbasedonrootpressure,apushonthewaterfromtherootsatthebottomoftheplant.Butrootpressureisnotnearlygreatenoughtopushwatertothetopsoftalltrees,Furthermore,theconifers,whichareamongthetallesttreeshaveunusuallylowrootpressures.Ifwaterisnotpumpedtothetopofatalltree,.andifitisnotpushed,tothetopofatalltree,thenwemayask.Howdoesitgetthere? Accordingtothecurrentlyacceptedcohesion-tensiontheory,waterispulledthere.Thepullonarisingcolumnofwaterinaplantresultsfromtheevaporationofwateratthetopoftheplant.Aswaterislostfromthesurfaceoftheleaves,anegativepressureortensioniscreated.Theevaporatedwaterisreplacedbywatermovingfrominsidetheplantinunbrokencolumnsthatextendfromthetopofaplanttoitsroots.Thesameforcesthatcreatesurfacetensioninanysampleofwater.areresponsibleforthemaintenanceoftheseunbrokencolumnsofwater.Whenwaterisconfinedintubesofverysmallbore,theforcesofcohestion(theattractionbetweenwatermolecules)arcsogreatthatthestrengthofacolumnofwatercompareswiththestrengthofa.steelwireofthesamediameter.Thiscohesivestrengthpermitscolumnsofwatertobepulledtogreatheightswithoutbeingbroken.1.Howmanytheoriesdoestheauthormention?(A)One(B)Two(C)Three(D)Four2.Thepassageanswerswhichofthefollowingquestions?(A)Whatistheeffectofatmosphericpressureonfoliage?(B)Whendodeadcellsharmplantgrowth?(C)Howdoeswatergettothetopsoftrees?(D)Whyisrootpressureweak?3.Theword"demonstrated"inline6isclose
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