六级阅读真题2001-2006

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1、2001年1月大学英语六级(CET-6)真题试卷PassageOneQuestions11to15arebasedonthefollowingpassage.Birdsthatareliterallyhalfasleep—withonebrainhemispherealertandtheothersleeping—controlwhichsideofthebrainremainsawake,accordingtoanewstudyofsleepingducks.Earlierstudieshavedocumentedhalfbrainsleepinawi

2、derangeofbirds.Thebrainhemispherestaketurnssinkingintothesleepstagecharacterizedbyslowbrainwaves.Theeyecontrolledbythesleepinghemispherekeepsshut,whilethewakefulhemisphere’seyestaysopenandalert.Birdsalsocansleepwithbothhemispheresrestingatonce.Decadesofstudiesofbirdflocksledresea

3、rcherstopredictextraalertnessinthemorevulnerable,endoftherowsleepers.Sureenough,theendbirdstendedtowatchcarefullyonthesideawayfromtheircompanions.Ducksintheinnerspotsshowednopreferenceforgazedirection.Also,birdsdozing(打盹)attheendofthelineresortedtosinglehemispheresleep,ratherthan

4、totalrelaxation,moreoftenthaninnerducksdid.Rotating16birdsthroughthepositionsinafourduckrow,theresearchersfoundouterbirdshalfasleepduringsome32percentofdozingtimeversusabout12percentforbirdsininternalspots.“Webelievethisisthefirstevidenceforananimalbehaviorallycontrollingsleepand

5、wakefulnesssimultaneouslyindifferentregionsofthebrain,”theresearcherssay.Theresultsprovidethebestevidenceforalongstandingsuppositionthatsinglehemispheresleepevolvedascreaturesscannedforenemies.Thepreferenceforopeninganeyeonthelookoutsidecouldbewidespread,hepredicts.He’sseenitinap

6、airofbirdsdozingsidebysideinthezooandinasinglepetbirdsleepingbyamirror.Themirrorsideeyeclosedasifthereflectionwereacompanionandtheothereyestayedopen.Usefulashalfsleepingmightbe,it’sonlybeenfoundinbirdsandsuchwatermammals(哺乳动物)asdolphins,whales,andseals.Perhapskeepingonesideoftheb

7、rainawakeallowsasleepinganimaltosurfaceoccasionallytoavoiddrowning.Studiesofbirdsmayofferuniqueinsightsintosleep.JeromeM.SiegeloftheUCLAsayshewondersifbirds’halfbrainsleep“isjustthetipoftheiceberg(冰山)”Hespeculatesthatmoreexamplesmayturnupwhenwetakeacloserlookatotherspecies.11.Ane

8、wstudyonbirds’sleephasrevealedthat______