06四级.docx

06四级.docx

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06四级

COLLEGEENGLISHTEST

—BandFour—

PartIWriting（30minutes）

PartIIReadingComprehension（SkimmingandScanning）（15minutes）

Directions:

Inthispart,youwillhave15minutestogooverthepassagequicklyandanswerthequestionsonAnswerSheet1.Forquestions1-7,choosethebestanswerfromthefourchoicesmarked［A］,［B］,［C］and［D］.Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.

AnimalsontheMove

Itlookedlikeascenefrom“Jaws”butwithoutthedramaticmusic.Ahugesharkwaslowlyswimmingthroughthewater,itstailswingingbackandforthlikethependulumofaclock.

Suddenlysensitivenerveendingintheshark’sskinpickedupvibrationsofastrugglingfish.Thesharkwasimmediatelytransformedintoadeadly,efficientmachineofdeath.Withmusclestaut,thesharkknifedthroughthewateratarapidspeed.Inaflashthesharkcaughtitsvictim,alargefish,initspowerfuljaws.Then,jerkingitsheadbackandforth,thesharktorehugechunksoffleshfromitsvictimandswallowedthem.Soontheactionwasover.

MovingtoSurvive

Inpursuingitsprey,thesharkdemonstratedinadramaticwaytheimportantroleofmovement,orlocomotion,inanimals.

Liketheshark,mostanimalsusemovementtofindfood.Theyalsouselocomotiontoescapeenemies,findamate,andexplorenewterritories.Themethodsoflocomotionincludecrawling,hopping,slithering,flying,swimming,orwalking.

Humanshavetheaddedadvantageofusingtheirvariousinventionstomoveaboutinjustabout几乎anykindofenvironment.Automobiles,rockets,andsubmarinestransporthumansfromdeepoceanstoasfarawayasthemoon.However,forotheranimalsmovementcameaboutnaturallythroughmillionsofyearsofevolution.Oneofthemostsuccessfulexamplesofanimallocomotionisthatoftheshark.Itsabilitytoquicklyzeroinonitspreyhasalwaysimpressedscientists.ButittookadetailedstudybyDukeUniversitymarinebiologistsS.A.Wainwright,F.Vosburgh,andJ.H.Hebranktofindouthowthesharksdidit.IntheirstudythescientistsobservedsharksswimminginatankatMarinelandinSaintAugustine,Fla.Moviesweretakenofthesharks’movementsandanalyzed.Studieswerealsomadeofsharkskinandmuscle.

SkinIstheKey

Thebiologistsdiscoveredthattheskinofthesharkisthekeytotheanimal’shighefficiencyinswimmingthroughthewater.Theskincontainsmanyfibersthatcrisscrossliketheinsideofabeltedradialtire.Thefibersarecalledcollagenfibers.Thesefiberscaneitherstoreorreleaselargeamountsofenergydependingonwhetherthefibersarerelaxedortaut.Whenthefibersarestretched,energyisstoredinthemthewayenergyisstoredinthestringofabowwhenpulledtight.Whentheenergyisreleased,thefibersbecomerelaxed.

TheDukeUniversitybiologistshavefoundthatthegreateststretchingoccurswherethesharkbendsitsbodywhileswimming.Duringthebody’sbackandforthmotion,fibersalongtheoutsidepartofthebendingbodystretchgreatly.Muchpotentialenergyisstoredinthefibers.Thisenergyisreleasedwhentheshark’sbodysnapsbacktheotherway.

Asenergyisalternatelystoredandreleasedonbothsidesoftheanimal’sbody,thetailwhipsstronglybackandforth.Thiswhip-likeactionpropelstheanimalthroughthewaterlikealivingbullet.

SourceofEnergy

Whatcausesthefiberstostoresomuchenergy?

InfindingtheanswertheDukeUniversityscientistslearnedthattheshark’ssimilaritytoabeltedradialtiredoesn’tstopwiththeskin.Justasaradialtireisinflatedbypressure,so,too,istheareajustundertheshark’scollagen“radials”.Insteadofairpressure,however,thepressureinthesharkmaybeduetotheforceofthebloodpressingonthecollagenfibers.

Whenthesharkswimsslowly,thepressureonthefibersisrelativelylow.Thefibersaremorerelaxed,andthesharkisabletobenditsbodyatsharpangles.Theanimalswimsthiswaywhenlookingaroundforfoodorjustswimming.However,whenthesharkdetectsanimportantfoodsource,somefantasticinvoluntarychangestakeplace.

Thepressureinsidetheanimalmayincreaseby10times.Thispressurechangegreatlystretchesthefibers,enablingmuchenergytobestored.

Thisenergyisthentransferredtothetail,andthesharkisoff.Therestofthestoryispredictable.

DolphinHasSpeedRecord

Anotherfastmarineanimalisthedolphin.Thisseagoingmammalhasbeenclockedatspeedsof32kilometers（20miles）anhour.Biologistsstudyingthedolphinhavediscoveredthat,liketheshark,theanimal’sefficientlocomotioncanbetracedtoitsskin.Adolphin’sskinismadeupinsuchawaythatitoffersverylittleresistancetothewaterflowingoverit.Normallywhenafishorotherobjectmovesslowlythroughthewater,thewaterflowssmo