大学英语四级考试Model Test ThreeWord文档下载推荐.docx

大学英语四级考试Model Test ThreeWord文档下载推荐.docx

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Comparedtotherestoftheuniverse,theEarthisverysmall.Ourplanetandeight（ormaybenine）othersorbittheSun,whichisonlyoneofabout200billionstarsinourgalaxy.Ourgalaxy,theMilkyWay,ispartoftheuniverse,whichincludesmillionsofothergalaxiesandtheirstarsandplanets.Bycomparison,theEarthismicroscopic.

Comparedtoaperson,ontheotherhand,theEarthisenormous.Ithasadiameterof7,926miles（12,756kilometers）attheequator,andithasamassofabout6×

1024kilograms.TheEarthorbitstheSunataspeedofabout66,638milesperhour（29.79kilometerspersecond）.Don'

tdwellonthosenumberstoolong,though;

toalotofpeople,theEarthisinconceivably,mind-bogglinglybig.Andit'

sjustafractionofthesizeoftheSun.

FromourperspectiveonEarth,theSunlooksverysmall.Thisisbecauseit'

sabout93millionmilesawayfromus.TheSun'

sdiameteratitsequatorisabout100timesbiggerthanEarth'

s,andaboutamillionEarthscouldfitinsidetheSun.TheSunisinconceivably,mind-bogglinglybigger.

ButwithouttheSun,theEarthcouldnotexist,inasense,theEarthisagiantmachine,fullofmovingpartsandcomplexsystems.Allthosesystemsneedpower,andthatpowercomesfromtheSun.

TheSunisanenormousnuclearpowersource-throughcomplexreactions,ittransformshydrogenintohelium,releasinglightandheat.Becauseofthesereactions,everysquaremeterofourplanet'

ssurfacegetsabout342WattsofenergyfromtheSuneveryyear.Thisisabout1.7×

1017Wattstotal,orasmuchas1.7billionlargepowerplantscouldgenerate.YoucanlearnabouthowtheSuncreatesenergyinHowtheSunWorks.

WhenthisenergyreachestheEarth,itprovidespowerforavarietyofreactions,cyclesandsystems.Itdrivesthecirculationoftheatmosphereandtheoceans.Itmakesfoodforplants,whichmanypeopleandanimalseat.LifeonEarthcouldnotexistwithouttheSun,andtheplanetitselfwouldnothavedevelopedwithoutit.

Toacasualobserver,theSun'

smostvisiblecontributionstolifearelight,heatandweather.

NightandDay

SomeoftheSun'

sbiggestimpactsonourplanetarealsoitsmostobvious.AstheEarthspinsonitsaxis,partsoftheplanetareintheSunwhileothersareintheshade.Inotherwords,theSunappearstoriseandset.Thepartsoftheworldthatareindaylightgetwarmerwhilethepartsthataredarkgraduallylosetheheattheyabsorbedduringtheday.

YoucangetasenseofhowmuchtheSunaffectstheEarth'

stemperaturebystandingoutsideonapartlycloudyday.WhentheSunisbehindacloud,youfuelnoticeablycoolerthanwhenitisn'

t.ThesurfaceofourplanetabsorbsthisheatfromtheSunandemitsitthesamewaythatpavementcontinuestogiveoffheatinthesummeraftertheSungoesdown.Ouratmospheredoesthesamethings-itabsorbstheheatthatthegroundemitsandsendssomeofitbacktotheEarth.

TheEarth'

srelationshipwiththeSunalsocreatesseasons.TheEarth'

saxistipsalittle-about23.5degrees.OnehemispherepointstowardtheSunastheotherpointsaway.ThehemispherethatpointstowardtheSuniswarmerandgetsmorelight--it'

ssummerthere,andintheotherhemisphereit'

swinter.Thiseffectislessdramaticneartheequatorthanatthepoles,sincetheequatorreceivesaboutthesameamountofsunlightallyear.Thepoles,ontheotherhand,receivenosunlightatallduringtheirwintermonths,whichispartofthereasonwhythey'

refrozen.

Mostpeoplearesousedtothedifferencesbetweennightandday（orsummerandwinter）thattheytakethemforgranted.Butthesechangesinlightandtemperaturehaveanenormousimpactonothersystemsonourplanet.Oneisthecirculationofairthroughouratmosphere.Forexample:

TheSunshinesbrightlyovertheequator.TheairgetsverywarmbecausetheequatorfacestheSundirectlyandbecausetheozonelayeristhinnerthere.

Astheairwarms,itbeginstorise,creatingalowpressuresystem.Thehigheritrises,themoretheaircools.Watercondensesastheaircools,creatingcloudsandrainfall.Theairdriesoutastherainfalls.Theresultiswarm,dryair,relativelyhighinouratmosphere.

Becauseofthelowerairpressure,airrushestowardtheequatorfromthenorthandsouth.Asitwarms,itrises,pushingthedryairawaytothenorthandthesouth.

Thedryairsinksasitcools,creatinghigh-pressureareasanddesertstothenorthandsouthoftheequator.

ThisisjustonepieceofhowtheSuncirculatesairaroundtheworld--oceancurrents,weatherpatternsandotherfactorsalsoplayapart.Butingeneral,airmovesfromhigh-pressuretolow-pressureareas,muchthewaythathigh-pressureairrushesfromthemouthofaninflatedballoonwhenyouletgo.Heatalsogenerallymovesfromthewarmerequatortothecoolerpoles.Imagineawarmdrinksittingonyourdesk--theairaroundthedrinkgetswarmerasthedrinkgetscolder.ThishappensonEarthonanenormousscale.

TheCoriolisEffect,aproductoftheEarth'

srotation,affectsthissystemaswell.Itcauseslargeweathersystems,likehurricanes,torotate.Ithelpscreatewestward-runningtradewindsneartheequatorandeastward-runningjetstreamsinthenorthernandsouthernhemispheres.Thesewindpatternsmovemoistureandairfromoneplacetoanother,creatingweatherpatterns.（TheCoriolisEffectworksonalargescale--itdoesn'

treallyaffectthewaterdrainingfromthesinklikesomepeoplesuppose.）

TheSungetsmuchofthecreditforcreatingbothwindandrain.WhentheSunwarmsairinaspecificlocation,thatairrises,creatinganareaoflowpressure.Moreairrushesinfromsurroundingareastofillthevoid,creatingwind.WithouttheSun,therewouldn'

tbewind.Therealsomightnotbebreathableairatall.

WaterandFire

TheSunhasahugeeffectonourwater.Itwarmstheoceansaroundthetropics,anditsabsencecoolsthewateraroundthepoles.Becauseofthis,oceancurrentsmovelargeamountsofwarmandcoldwater,drasticallyaffectingtheweatherandclimatearoundtheworld.TheSunalsodrivesthewatercycle,whichmovesabout18,757cubicmiles（495,000cubickilometers）ofwatervaporthroughtheatmosphereeveryyear.

Ifyou'

veevergottenoutofaswimmingpoolonahotdayandrealizedafewminuteslaterthatyouweredryagain,youhavefirsthandexperiencewithevaporation.Ifyou'

veseenwaterformonthesideofacolddrink,you'

veseencondensationinaction.Theseareprimarycomponentsofthewatercycle,alsocalledthehydrologiccycle,whichexchangesmoisturebetweenbodiesofwaterandlandmasses.Thewatercycleisresponsibleforcloudsandrainaswellasoursupplyofdrinkingwater.

1.HowmanyEarthscouldfitinsidetheSun?

[A]Onemillion.

[B]93million.

[C]Twomillion.

[D]100million.

2.Earthwouldnothavedevelopedwithout______.

[A]water

[B]fertilizer

[C]soil

[D]theSun

3.Whatdoesouratmospheredo?

[A]ItabsorbstheheatfromthegroundandsendsittotheSun.

[B]ItabsorbstheheatfromtheSunandemitsitbacktotheEarth.

[C]ItabsorbstheheatfromtheSunandemitsitthesameway.

[D]ItabsorbstheheatthegroundemitsandsendssomeofitbacktotheEarth.

4.______receivesaboutthesameamountofsunlightallyear.

[A]Thepoles

[B]Theequator

[C]Thenorthtemperatezone

[D]Thesouthtemperatezone

5.Airrushestowardtheequatorfromthenorthandsouth______.

[A]becauseofthedryair

[B]becauseofthecoolair

[C]becauseofthelowerairpressure

[D]becauseofthehigherairpressure

6.Whatdoesn'

ttheCoriolisEffectcause?

[A]Westward-runningtradewinds.

[B]Hurricanes.

[C]Thewaterdrainingfromthesink.

[D]Eastward-runningjetstreams.

7.TheSunhascloselyrelationtocreate______.

[A]wind

[B]theair

[D]fire

8.TheSunhasahugeeffecton______.

9.Ifyou'

veseen______.

10.Thewatercycleisresponsibleforclouds,rainand______.

PartⅢListeningComprehension

SectionA

Inthissection,youwillhear8shortconversationsand2longconversations.Attheendofeachconversation,oneormorequestionswillbeaskedaboutwhatwassaid.Boththeconversationandthequestionswillbespokenonlyonce.Aftereachquestiontherewillbeapause.Duringthepause,youmustreadthefourchoicesmarked[A],[B],[C]and[D],anddecidewhichisthebestanswer.ThenmarkthecorrespondingletteronAnswerSheet2withasinglelinethroughthecentre.

Questions11to18arebasedontheconversationyouhavejustheard.

11.[A]Atthedepartmentstore.

[B]Attheoffice.

[C]Intherestaurant.

[D]Inthedrugstore.

12.[A]Themanshouldn'

texpecthertogoalong.

[B]Shedoesn'

tthinkshehasenoughmoney.

[C]She'

llgoeventhoughthemovieisbad.

[D]Themanshouldcountthenumberofpeoplegoing;

13.[A]Shewasn'

treallystudying.

[B]Shehadn'

tfinishedwritingherarticles.

[C]Shehadfurnishedherhouse.

[D]She