大学英语六级模拟题

大学英语六级模拟题5套一、写作(共1题，合计15分)MyViewonSpendingCrazeDuringGraduation_____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________阅读理解(共4题，合计35分)根据以下内容答复37-46题Whenstudyinghumantalent,thetemptationisusuallytoconcentrateontheupperreaches.Understandablyso:wealladmiretheEinsteinsandMozartsofthisworldand36toimitatethem.Incomparison,studyingtheoppositeendofthespectrummightseempointless,patronizing(摆出恩赐态度的)ordownrighttasteless.Lackofintelligenceisshamefulenoughwithouttreatingpeoplelikelabrats.Yetitoftentakesadifferentviewpointtofindnewinsightsintoanoldproblem.Stupidityistooimportantandinterestingtoignore.Thescienceofstupidityisproducingresultsthat37ourconceptsofintelligenceandthatshouldbehumblingformanyofthesmartpeoplewhoruntheworld.Itturnsoutthatatendencyforentertaining38,foolishorillogicalideasisnotnecessarilytheresultofalowIQ.Thismeasureofintelligenceislargely39ofrationality.Justbecauseyouscoreonthehighendofonescaledoesn'tmeanthatyouwon'tfallatthebottomoftheother.Importantly,nooneis40tothebiasesthatleadtostupiddecisions.YetourrespectforIQandeducationmeansthatitiseasytorestonthelaure/s(桂冠)ofourqualificationsandassumethatweare,bydefinition,notstupid.Thatcanbe41onapersonallevel:regardlessofIQ,peoplewhoscorebadlyonrationalitytestsaremorelikelytohaveunplannedpregnanciesorfallintoseriousdebt.Largescalestupidityisevenmoredamaging.Businessculturesthat42encourageit,forexample,mayhavecontributedtotheeconomiccrisis.Indeed,theeffectsmayhavebeensodamagingpreciselybecausebanksassumedthatintelligentpeopleactlogicallywhileatthesametimerewardingrashbehaviorbasedonintuitionratherthan43.Asoneresearcherputsit:"Themoreintelligentsomeoneis,themoredisastroustheresultsoftheirstupidity".Thesamesurelyappliestopoliticians:thetenthanniversaryoftheinvasionofIraqservesasa44thatcleverpeoplecandomonumentallystupidthings.Ifwewanttoavoidmakingsimilarmistakesinthefuture,everybody--especiallythemostintelligentandpowerful--woulddowelltohumbly45theirownweaknesses.ToquoteOscarWilde:"Thereisnosinexceptstupidity."A)acknowledgeB)aspireC)challengeD)commemorateE)damagingF)deliberationG)immuneH)inadvertentlyI)independentJ)negligibleK)nominationL)DperpetuallyM)rashN)recipientO)reminder36题_____37题_____38题_____39题_____40题_____41题_____42题_____43题_____44题_____45题_____46题_____根据以下内容答复47-56题Technology,Costs,LackofAppealSlowE-TextbookAdantian[A]TextbooksareoftenaluxuryforcollegeseniorVatellMartin.TheaccountingmajoratVirginiaStateUniversitygotbyinseveralcourseswithstudygroupsandprofessors'lectures."It'snotthatIdidn'twanttobuy,"hesays."Sometimes,Ijustdidn'thavethemoneyfora$200book."VSUknowsMartinisn'ttheonlyone.Morethanhalfofitsstudentsroutinelyskipbuyingtextbooks.Forasolution,theschoolisturningtoe-textbooks.[B]VSUpartneredwithFlatWorldKnowledge,astart-uppublisherthatproducesexclusivelywrittene-bookswith"open"contentthatcanbemodifiedbyprofessors.Inatrialwith14businesscourses,studentswouldberequiredtopay$20andreceiveaFlatWorlde-bookanddigitallearningsupplements.Theuniversityandalocalgranthavebeencoveringthecost,sofar."That'snothing.It'swhatIputinmygastank,"saysMartin,whoparticipatedinthetrial."IfIwaswalkingintoadiscussiononatopic,Icanjustdownloadandtakeoutthebookandreaditonmyphone."[C]Withtheirpromiseofubiquity(无处不在),convenienceandperhapsaffordability,e-textbookshavearrivedinfitsandstartsthroughoutcollegecampuses.Andpublishersandbookresellersarespendingmillionsattractingstudentstotheironlinestoresande-readerplatformsasmobiletechnologyimprovesthereadabilityofthematerialondevicessuchastabletcomputers.SiliconValleystart-ups,suchasInklingandKno,arealsoaggressivelyreinventingtextbookswithinteractivegraphics,videosandsocial-mediafeatures.[D]Despiteemergingattemptsatinnovation,theindustryhasbeenslowedbyclumsytechnology,thelastingappealofprintbooks,skepticalstudentswhosearchonlineforcheaperalternatives,andcustomerconfusionstemmingfromtoomanyme-tooe-textbookplatformsthathavefailedtostandout.[E]ThelateSteveJobs,founderofApple,believedtextbookstobean$8billionmarketripefor"digitaldestruction,"biographerWalterIssacsonwritesinSteveJobs.AppleisexpectedtomakeanannouncementThursdayaboutitsneweducationproducts.Themarketissmallbutgrowing.Salesfore-textbooksintheU.S.highereducationmarketgrew44.3%to$267.3millionin2023,accordingtoSimbaInformation,apublishingindustryresearchfirm.Printstillrules[F]Sofar,studentshavebeenlessthanimpressedandmorelikelytochooseprintbooks.About11%ofcollegestudentshaveboughte-textbooks,accordingtomarketresearchfirmStudentMonitor.Availabilityisn'tthechiefproblem.Mostpopulartextbookshaveadigitalversion,andthey'reavailableonline.Butstudentshavelargelystayedawaybecausethemostreadilyavailabletechnologytoday--PDF(portabledocmnentformat)orotherdocumentreaderversionsoftheprintbook—isclumsyandeye-strainingtoread.[G]WhenAndreaSoto,afreshmanbiologymajorattheUniversityofMaryland,boughtPrinciplesofBiology,the$192pricetagcamewithafreeonlineversion.Sheprefersthetouchablepresenceofathickbookonherlap."Youcan'thighlightorunderlinethingsinthee-book.Ifinditmoreofatrouble,"shesays.However,digitalbooksaren'tnecessarilycheaper,either.Whilepricedlowerthannewprintbooks,they'reoftenmoreexpensivethanbuyingorrentingusedbooksonline,saysKathyMickey,ananalystatSimba.AfederallyfundedpilotstudyatDaytonaStateCollegeinFloridafoundthatsomestudentswhorentedane-textbookpaidonlyadollarlessthanstudentswhoboughtaprintedition.Ande-textbookuserscouldn'tsellthebookbackaftertheclassended.[H]Despitee-textbooks'shortcomings,mostagreethattheprintmarketisripeforatechnologicaloverhaul(彻底改革).Pricesofnewbooksarerisingsharply.Authorscomplainaboutusedbooksalesthatdon'tgenerateroyalties.ProfessorsandstudentsaxeannoyedatneweditionsthatseeminglyaddlittleincontentVSthepreviousone.[I]"Thisisanindustrythat'sfailingeveryone--parents,authors,professors,andstudents,"saysBradWheeler,chiefinformationofficeratIndianaUniversity,whichisrunningaprogramthatdistributescheapere-textbooksbutrequiresallstudentsintheclasstobuy.Publishersareeagerforaquickertransitiontotheformatbecausee-textbookscostlesstopublishandwouldgenerateincomefromeverystudentwhobuysone.Digitalbookscan'tberesold,atleast,notlegally."We'dpreferthatallofittogodigital,"saysVineetMadan,seniorvicePresidentofnewventuresatMcGraw-HillEducation."Thereisn'tasecondarymarketfore-books."Seekingmarketniche(商机)[J]Ifcurrente-textbooksaremostlyunappealing,what'snext?Likeonlinemusicinitsinfancy,thetextbookindustry'skeyplayers--publishers,resellers,bookstores,techcompanies,evensomeuniversities--areallscramblingtooffertheirdigitalsolutions,aneffortthathasensifiedwiththearrivaloftabletcomputersandappstores."Everybodyandtheirbrothersarecomingoutwithane-bookplatform,"saysIamWilliams,directorofstrategiclearningsolutiousatWiley,atextbookpublisher.[K]Theyallagreeononething:Thequalityofe-textbooksmustimprovedramatically.Morevalueadded,interactivefeatureswillkeepstudentsinterestedandspursales,theysay.Tabletcomputersareakeystimulusinthisendeavor.AtKno,tabletshaveallowedtheSantaClara,Cpanytoembedinteractivetoolsontoanexistinge-textbookinamoreintuitiveway,forexample,theabilitytowritedirectlyonthebookwithafingerstrokeortaponakeywordfornotes."Tabletwasaneededdevelopment,"saysKno'sfounderOsmanRashid.Despitethreatstotheirprintbooksales,universitybookstoresarealsocomingaroundtoembracinge-books.Follett,whichruns930universitybookstoresinNorthAmerica,launchedFollettCafeScribelastyear,acloud-baseddigitaltextbookplatform.Publishersnotonsidelines[L]Textbookpublishersarepartneringwithuniversitiesforexclusivetrials,buyingstakesinstart-upsanddevelopingtheirowntechnologies.Lastyear,publisherCengagelaunchedMindTap,ane-book/digitallearningwebsitethatisnowbeingtriedbyabout50professors,saysBillRieders,Cengage'sexecutivevicePresidentofglobalnewmedia.Insteadoftablesofcontent,MindTapprovides"alearningpath"thatstudentscanaccessfortext,multimedia,self-assessmenttools,quizzesandnotesharing.[M]Pearsonhasintroducedacompetingproduct,OpenClass.Thecloud-basedwebsitemeansstudentscanaccessinformationwhereverthere'sanonlineconnection--featuressocialnetworking,andworkswithGoogleAppsforEducation.ReedCollegeinPortland,Ore.,isoneofseveraluniversitiesthatwilltestOpenClassthisfall.[N]TheCourseLoadtrialhasbeeninplacesince2023onalimitedbasis,withstudentsreceivingfreebooks.Ithasbeenexpandedto130coursesthisspringsemester.StudentsnowpayadiscountedpriceforaccesstoCourseLoadbooksandlearningkits,typically"60%to70%"cheaperthannewprintbooks,Wheelersays.Inexchange,studentsmustpayafeetoenroll.Despitethelackofflexibility,schoolofficialsandstudentshaveembracedthelow-costapproach,hesays.47Thedevelopmentoftabletcomputersisnecessarytoimprovethee-textbook'squality.48It'sdifficulttomakenotesonthedigitalversion,soAndreaSotochosetheprintbook.49Duetothemobiletechnology,readabilityonelectronicequipmentbecomesbetter50InMindTap,eachfunctioncanbeaccessiblethrough"alearningpath"ratherthanthetablesofcontent.51PublisherslikeVineetMadanprefere-textbooksbecausetheycouldn'tberesoldlegally.52OpenClassallowsstudentstogetinformationwherevertheycangetconnectedtotheInternet.53ManystudentsinVSUhatetobuyexpensivetextbooks,thustheschoolpromotese-textbookstostudents.54StudentscangetadiscountedpricefromCourseLoadbooksbuttheyshouldpaytheenrollmentfee.55Thee-textbookpublisherscooperatewithuniversitiestoachievesoletryouts.56Althoughe-textbookindustrymakesanefforttoinnovate,it'sstillrestrictedfromdeveloping.Questions57-61arebasedonthefollowingpassage.Rumorshaveswirledforyearsaboutthemysticalphone,whichFacebooKintroducedatitsheadquarterstoday.ForthefinancialsakeofFacebook,it'simperativethatthenewphone--manufacturedbyHTC,carriedbyAT&TandsportinganAndroidoperatingsystem--sellswell.It'sthelinchpin(关键)inthesocial-networkingcompany'spursuitofmobileads,The$99phonegoesonsaleAprill2.Thephone/servicefeaturesHome(facebook,corn/home),downloadablesoftwarethatbringstheFacebookexperiencetoseveralAndroiddevices:HTCOneX,HTCOneX+,SamsnngGalaxySIIIandSamsumgGalaxyNoteII.Atfirstblush,thenewphonecouldfindareceptiveaudienceamongthennder-25crowd,whichiscomfortablewithhavingtheirmobiledeviceswithinreachatalltimes.Facebookchafesatsuggestionsthatteensandtwentysomethingsareleavingthesocialnetwork,soaphoneimmersedinnewsupdatesandotherFacebookfeaturesmightgooverwell.Facebook,theNo.2mobile-adpublisherintheU.S.behindGoogle,lastyearaccountedfor9.5%ofthe$4.1billionmobileadmarket.It'sexpectedtotakeI3%ofthe$7.3billionmarketthisyear,estimatesresearchereMarketer.Aphonecould"hardwire"theFacebookexperienceonamobiledevice,increasingconsumers'timeontheservice,analystssay.Buttheexperiencehastobemorethanabrandeddevice,theysay.BrandedphonesfromBarclaysandMaryKaydidnotfarewell."Itcan'tbejustaboutthehardware,"saysPhillipRedman,mobileanalystatGartner."Itcandotwothingsforsuccess:Changethebusinessmodelandgiveitawaytoitsbestusers;ordesignitforlow-costorno-costcallsamongFacebookfriends."Facebook'sentryisoneinaglut(供过于求)ofrecentsmartphonecontestants.NewmodelsfromSamsung(Galaxy$4),HTC(One)andBlackBerry(theQ10keyboarD.highlightabumperspringcrop.Apple'srumorediPhone5SoriPhone6lurksintheshadows,"Thehandsetmarketisverycompetitive,"saysClarkFredricksen,vicepresidentateMarketer."Samsung,AppleandAndroidallaregainingmarketshare,andboastcomputingplatformstofeedinto(the)mobilemarket.ItremainstobeseenifFacebookwillgainpopularity."Facebookboasts1billionmembers,30%ofwhicharemobile-onlyusers,accordingtomarketresearcherComScore.ItwasalsotheNo.1mobileappintheU.S.inFebruaryintermsofengagement,accountingfor24%ofalltimespentonmobileapps--27%,ffyouincludeInstagram.57WhyisthenewphonesocrucialtoFacebook?A.Becauseithelpsmakemoney.B.Becauseitisessentialtothecompany'sgoalofmobileads.C.Becauseitcanhelpthecompanygetoutoftherumorsaboutit.D.Becauseitisintroducedatthecompany'sheadquarters.58Theunder-25groupofpeopleA.arenotthetargetcustomersofFacebookB.knowlittleaboutsocialnetworkC.usemobilephonesallthetimeD.spendmoretimeoncomputersthanonmobiledevices59WhatcanbeinferredfromthefigurespresentedbyeMarketerthisyear?A.Themobileadsmarketisshrinking.B.FacebookwilltakeoverGoogleinthemobileadsmarket.C.FacebookwillstillbetheNo.2mobile-adpublisher.D.Themobileadsmarketisexpanding.60AccordingtoClarkFredricksen,theprospectofthenewphoneA.issurelybrightB.isnotclearyetC.isgloomyduetoheatedcompetitionD.interestsallthephoneusers61Whatcanbeinferredfromthelassparagraph?A.InstagramcanbeseenaspartoftheFacebook.B.Mobileappsareverytime-consuming.C.FacebookhasthelargestnumberofuserscomparedwithotherMobileapps.D.InstagramistherealNo.1Mobileapp.Questions62-66arebasedonthefollowingpassage.ThemostpromisingeffortinyearstorestorefairnessandhopetbtheimmigrationsystembeginsWednesday,whentheObamaadministrationwillstartacceptingapplicationsfromyoking,undocumentedimmigrantswhowanttobeshieldedfromdeportation(驱逐出境)sotheycanbefreetoworkandgotoschool.Theprogramtohaltdeportationsislimited,hedgedbydetailedrulesandnottobeconfusedwithbroadimmigrationreform,whichisoutofreachatatimewhenresentmentagainsttheundocumentedrunshighinWashingtonandinthestates.Butanyprogressawayfromindiscriminateimmigrationenforcement,andtowardopeningpathwaystoafullerinvolvementinsociety,isworthnotingandcelebrating.Undertheprogram,applicantsmusthavebeenbroughttotheUnitedStatesbeforeturning16,beunder31,havecleanrecordsandhavelivedhereforatleastthelastfiveyears.Thosewhoareacceptedwillnotbelegalized,eveniftheyaregivenpermissiontowork.Theywillinsteadbegrantedtwo-yeardeferrals(延期)ofdeportation,whicharerenewable.Byoneestimate,1.7millionofthecountry's11millionundocumentedimmigrantsmayqualify.AnnouncedbyPresidentObamainJune,theprogramisnotthelegalizationorpathtocitizenshipthatmillionsarelongingforanddeserve.It'ssimplyadecisionbytheDepartmentofHomelandSecurity,atPresidentObama'sinstruction,togetitsenforcementprioritiesrightfocusingonremovingcriminalsandotherswhothreatencommunitysafety,notthelaw-abiding,hard-workingyoungpeoplewhoposenothreatandcannotbeblamedfortheirunauthorizedstatus.Therearetwomajorworriesastheprogramunfolds.OneiswhetherCitizenshipandImmigrationServices,theagencythatwillruntheprogram,canhandletheadministrativeload.AlejandroMayorkas,thedirector,sayshisagencyisinvestinginstaffingandtraining,helpedalongbythe$465feechargedtoeachapplicant.Theagencydependsentirelyonfees.Theotherfearisthatapplicantswillfallpreytofraud.Immigrationlawisextremelycomplicated,whichdishonestconsultants,knownas"notarios",takefulladvantageof.Applicantswhoarerejectedhavenorighttoappealandwillstillriskdeportation,especiallythosewhosepaperworkwasfalsified(伪造的).Thecitizenshipagencyneedstodoallitcantoeducateapplicantsandpreventfrauds.Thentherewillbetheattacksfromthosewhocannotstomachanythinglessthantheejectionofeverylastimmigrantwholackslegalstatus.ThisharshnessisexemplifiedbySenatorJeffSessions,RepublicanofAlabama,whodenouncedtheprogramonWednesday."Icannotoverstatethetragedyofthis,"hesaid,doingjustthat.Hisinabilitytodistinguish"criminalaliens"fromtheyoungstriverstheUnitedStatesneedsisthereasonthecountryhasbeenforcedintoadministrativehalf-measures,ratherthanreallegislativereform.62Accordingtothepassage,theObamaadministrationwillA.protectundocumentedimmigrantsfromdeportationB.offeryoungimmigrantsfreeeducationandjobtrainingC.undergobroadimmigrationreformacrossthestatesD.makeprogresstowardfairimmigrationenforcement63Underthenewimmigrationprogram,applicantsthatareacceptedA.canbebroughttotheUnitedStatesbefore16B.canliveintheUnitedStatesforfiveyearsC.willbeallowedtoseekjobsintheU.S.D.willbeentitledtoU.S.citizenshipintwoyears64Whatdoestheauthorsayaboutthenewimmigrationprogram?A.Itopensupalegalpathtocitizenshipforundocumentedimmigrants.B.Itgrantsauthorizedstatustothehard-workingyoungimmigrants.C.ItendowsPresidentObamawiththeenforcementprioritiesright.D.Itfocusesondrivingouttheimmigrantswithcriminalrecords.65Whatisonemajorconcernwiththelaunchofthenewimmigrationprogram?A.CitizenshipandImmigrationServiceshasnoenoughfundstoruntheprogram.B.CitizenshipandImmigrationServiceswillchargetheapplicantsarbitrarily.C.Immigrationlawcanbetoocomplicatedtobeexplainedtotheapplicants.D.Theapplicantscaneasilyfallintothetrapofdishonestconsultants.66Whydoesn'ttheUnitedStatestakethereallegislativeimnu'grationreform?A.Theimmigrationagencycannothandletheadministrativeload.B.TheUnitedStatesregardsalltheimmigrantscriminalaliens.C.SenatorJeffSessionshighlightsthelossesillegalimmigrantsmayincur.D.JeffSessionsbearsresentmentagainstalltheundocumentedimmigrants.四、翻译(共1题，合计15分)67中国是世界四大文明古国之一，幅员辽阔(vastterritory)，山河壮丽，物产丰富，历史文化悠久。五干年的人文创造(humanisticcreativity)和天开万物造就的自然景观为我们留下了景象骄人、数量繁多的名胜古迹，创造了辉煌的文化艺术。中国位于亚洲东部、太平洋西岸，面积960万平方公里。中国人口约13亿，共有56个民族，是世界上人口最多的国家。青藏高原(TheQinghai-TibetPlateau)是海拔最高的高原，喜马拉雅山系(Himalayas)是世界上最大的山系，其主峰珠穆朗玛峰是世界上最高的山峰。PartIListeningComprehension(30minutes)SectionADirections:Inthissectionyouwillhear10shortconversations.Attheendofeachconversation,aquestionwillbeaskedaboutwhatwassaid.Boththeconversationandthequestionwillbespokenonlyonce.Aftereachquestiontherewillbeapause.Duringthepause,youmustreadthefourchoicesmarkedA.,B.,C,andD.,anddecidewhichisthebestanswer.ThenmarkthecorrespondingletterontheAnswerSheetwithasinglelinethroughthecenter.1.A.Wherehasthewomanbeen?B.Whatdoesthewomanmeanbyherquestion?C.Whydidthewomanasksuchaquestion?D.Whydoesthewomanwonderabouthim?2.A.GivingalectureB.WashingC.MeetinghersisterD.Cleaning3.A.6:55B.7:05C.7:25D.7:154.A.TotherestaurantB.HomeC.TothemovietheaterD.Tohiswork5.A.Thewomanshouldhavefinishedherprojectbynow.B.Thewomanshouldworkonherprojectforonemoreweek.C.Thewomanshouldn'thavespentaweekonherproject.D.Thewomanhasbeenworkingataveryfastpace.6.A.GotothepartiesB.GoforaridewiththemanC.StudyforherexamD.Changeherclothes7.A.AtarestaurantB.AtaconferenceroomC.AtadrugstoreD.Ataclinic8.A.6:00B.5:10C.5:00D.5:159.A.SmokeB.OfferthewomanacigaretteC.5:10D.Putouthiscigarette10.A.Thewoman'sbossdidn'tknowshewaslateforwork.B.Thewoman'sbossaskedwhyshewasn'tthereontime.C.Thewomanisusuallypunctual.D.Thewoman'sbosswantshertokeepahabitofbeingontime.SectionBDirections:Inthissection,youwillhear3shortpassages.Attheendofeachpassage,youwillhearsomequestions.Boththepassageandthequestionwillbespokenonlyonce.Afteryouhearaquestion,youmustchoosethebestanswerfromthefourchoicesmarkedA.,B.,C.andD.,anddecidewhichisthebestanswer.ThenmarkthecorrespondingletterontheAnswerSheetwithasinglelinethroughthecenter.PassageOneQuestions11to13arebasedonthepassageyouhavejustheard.11.A.Irontools.B.SnowshoesC.PoliticalwaysD.Gunsforhunting12.A.TraininganimalsB.HuntinganimalsC.PlantingcropsD.Buildinghouses13.A.ThenewsettlerssurvivedtheharshwintersthankstotheIndians'help.B.Thenewsettlersintroducedtothenativescornandbeans.C.ThenativestriedtomakethelifeofthenewsettlersresemblethelifetheyoncehadinEngland.D.LifeinthenewworldwasnotlikewhattheSpanishexplorershadreported.PassageTwoQuestions14to16arebasedonthepassageyouhavejustheard.14.A.Theywerechildren'sfavoritetoys.B.Theywerefirstmadeofwoodorstone.C.Theyweremeanttobringgoodluck.D.TheywereinventedinGreece.15.A.WoodenandclaydollsB.RagdollsC.StonedollsD.Fashiondolls16.A.Around1700B.Around1800C.Around1900D.Around1600PassageThreeQuestions17to20arebasedonthepassageyouhavejustheard.17.A.AsasoldierB.AsadramatistC.AsapoetD.Asatranslator18.A.1912B.1922C.1921D.191119.A.AlmostthreeyearsB.ThreeyearsC.FouryearsD.Almostfouryears20.A.5B.4C.2D.3SectionC(CompoundDictation)略PartIIReadingComprehension(35minutes)Directions:Thereare4readingpassagesinthispart.Eachpassageisfollowedbysomequestionsorunfinishedstatements.ForeachofthemtherearefourchoicesmarkedA.,B.,C.andD.YoushoulddecideonthebestchoiceandmarkthecorrespondingletterontheAnswerSheetwithasinglelinethroughthecenter.Questions21to25arebasedonthefollowingpassage:Foralltheirgreatdiversityofshapesandsizes,glacierscanbedividedintotwoessentialtypes:valleyglaciers,whichflowdownhillfrommountainsandareshapedbytheconstraintsoftopography(地貌),andicesheets,whichflowoutwardinalldirectionsfromdome—likecentersofaccumulatedicetocovervastexpanseofterrain.Whatevertheirtype,mostglaciersareremnantsofgreatshroudsoficethatcoveredtheeartheonsago.Inafewoftheseglacierstheoldesticeisveryancientindeed;theageofpartsoftheAntarcticsheetmayexceed500,000years.Glaciersareborninrockywombabovethesnowline,wherethereissufficientwintersnowfallandsummercoldforsnowtosurvivetheannualmelting.Thelonggestationperiodofaglacierbeginswiththeaccumulationandgradualtransformationofsnowflakes.Soonaftertheyreachtheground,complexsnowflakesarereducedtocompact,roughlysphericalicecrystals,andthebasiccomponentsofaglacier.Asnewlayersofsnowandfirn,snowthatsurvivesthemeltingoftheprevioussummer,accumulate,theysqueezeoutmostoftheairbubblestrappedwithinandbetweenthecrystalsbelow.Thisprocessofrecrystallizationcontinuesthroughoutthelifeoftheglacier.Thelengthoftimerequiredforthecreationofglaciericedependsmainlyuponthetemperatureandtherateofsnowfall.InIceland,wheresnowfallisheavyandsummertemperaturesarehighenoughtoproduceplentyofmelt—water,glaciericemaycomeintobeinginarelativelyshorttime—say,tenyears.InpartsofAntarctica,wheresnowfallisscantandtheiceremainswellbelowitsmeltingtemperatureyearround,theprocessmayrequirehundredsofyears.Theicedoesnotbecomeaglacieruntilitmovesunderitsownweight,anditcannotmovesignificantlyuntilitreachesacriticalthickness—thepointatwhichtheweightofthepiled—uplayersovercomestheinternalstrengthoftheiceandthefrictionbetweentheiceandtheground.Thiscriticalthicknessisabout60feet.Thefastestmovingglaciershavebeengaugedatnotmuchmorethantwoandahalfmilesperyear,andsomecoverlessthan1/100inchinthatsameamountoftime.Butnomatterhowinfinitesimaltheflow,movementiswhatdistinguishesaglacierfromameremassofice.21.Whichofthefollowingisthemostappropriatedefinitionofglacier?A.Glaciersfallintotwobasiccategories:valleyglaciersandicesheets.B.Glaciersarehugemassesoficethatmoveundertheirownweight.C.Glacierseitherflowdownhillfrommountainsorflowoutwardinalldirectionsfromdome—likecentersofaccumulatedice.D.Glaciersareprimarilyformedintherockymountaintopsabovethesnowline.22.Whatisimpliedinthepassage?A.Glacierscanbedividedintomanycategoriesaccordingtotheirshapesandsizes.B.Icesheetsmovefasterthanvalleyglaciers.C.IttakeslongerforglacierstoforminAntarcticathaninIceland.D.Valleyglaciersarenotasoldasicesheets.23.WhydoestheauthormentiontheformationofglaciersinIcelandinthethirdparagraph?A.Heavysnowfallandhighsummertemperaturesmakeglacierscomeintoexistenceinarelativelyshortperiodoftim