托福阅读真题10篇.docx

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1、1995年托福阅读真题Questions1-13Atmosphericpressurecansupportacolumnofwaterupto10metershigh.Butplantscanmovewatermuchhigher,thesequoiatreecanpumpwatertoitsverytop,morethan100metersabovetheground.Untiltheendofthenineteenthcentury,themovementofwaterintreesandothertallplantswasamystery.Somebota

2、nistshypothesizedthatthelivingcellsofplantsactedaspumps,Butmanyexperimentsdemonstratedhatthestemsofplantsinwhichallthecellsarekilledcanstillmovewatertoappreciableheights.Otherexplanationsforthemovementofwaterinplantshavebeenbasedonrootpressure,apushonthewaterfromtherootsatthebottomof

3、theplant.Butrootpressureisnotnearlygreatenoughtopushwatertothetopsoftalltrees.Furthermore,theconifers,whichareamongthetallesttrees,haveunusuallylowrootpressures.Ifwaterisnotpumpedtothetopofatalltree,andifitisnotpushedtothetopofatalltree,thenwemayask,Howdoesitgetthere?Accordingtothecu

4、rrentlyacceptedcohesion-tensiontheory,waterispulledthere.Thepullonarisingcolumnofwaterinaplantresultsfromtheevaporationofwateratthetopoftheplant.Aswaterislostfromthesurfaceoftheleaves,anegativepressure,ortension,iscreated.Theevaporatedwaterisreplacedbywatermovingfrominsidetheplantinu

5、nbrokencolumnsthatextendfromthetopofaplanttoitsroots.Thesameforcesthatcreatesurfacetensioninanysampleofwaterareresponsibleforthemaintenanceoftheseunbrokencolumnsofwater.Whenwaterisconfinedintubesofverysmallbore,theforcesofcohesion(theattractionbetweenwatermolecules)aresogreatthatthes

6、trengthofacolumnofwatercompareswiththestrengthofasteelwireofthesamediameter.Thiscohesivestrengthpermitscolumnsofwatertobepulledtogreatheightswithoutbeingbroken.1.Howmanytheoriesdoestheauthormention?(A)One(B)Two(C)Three(D)Four2.Thepassageanswerswhichofthefollowingquestions?(A)Whatisth

7、eeffectofatmosphericpressureonfoliage?(B)Whendodeadcellsharmplantgrowth?(C)Howdoeswatergettothetopsoftrees?(D)Whyisrootpressureweak3.Theword"demonstrated"inline5isclosestinmeaningto(A)ignored(B)showed(C)disguised(D)distinguished4.Whatdotheexperimentsmentionedinlines4-6prove?(A)Plants

8、temsdiewhend