托福TPO25阅读完整原文文本Word下载.docx
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butmanysmalleronesarefoundinthenorthernplains.
ThegreatheightofMartianvolcanoesisadirectconsequenceofthe
planet’slowsurfacegravity.Aslavaflowsandspreadstoformashield
volcano,thevolcano’seventualheightdependsonthenewmountain’sabilityto
supportitsownweight.Thelowerthegravity,thelessertheweightandthe
greatertheheightofthemountain.ItisnoaccidentthatMaxwellMonsonVenus
andtheHawaiianshieldvolcanoesonEarthrisetoaboutthesameheight(about
10kilometers)abovetheirrespectivebases-EarthandVenushavesimilarsurface
gravity.Mars’ssurfacegravityisonly40percentthatofEarth,sovolcanoes
riseroughly2.5timesashigh.AretheMartianshieldvolcanoesstillactive?
Scientistshavenodirectevidenceforrecentorongoingeruptions,butifthese
volcanoeswereactiveasrecentlyas100millionyearsago(anestimateofthe
timeoflasteruptionbasedontheextentofimpactcrateringontheirslopes),
someofthemmaystillbeatleastintermittentlyactive.Millionsofyears,
though,maypassbetweeneruptions.
AnotherprominentfeatureofMars’ssurfaceiscratering.TheMariner
spacecraftfoundthatthesurfaceofMars,aswellasthatofitstwomoons,is
pittedwithimpactcratersformedbymeteoroidsfallinginfromspace.Asonour
Moon,thesmallercratersareoftenfilledwithsurfacematter-mostly
dust-confirmingthatMarsisadrydesertworld.However,Martiancratersget
filledinconsiderablyfasterthantheirlunarcounterparts.OntheMoon,
ancientcraterslessthan100metersacross(correspondingtodepthsofabout20
meters)havebeenobliterated,primarilybymeteoriticerosion.OnMars,there
arerelativelyfewcraterslessthan5kilometersindiameter.TheMartian
atmosphereisanefficienterosiveagent,withMartianwindstransportingdust
fromplacetoplaceanderasingsurfacefeaturesmuchfasterthanmeteoritic
impactsalonecanobliteratethem.
AsontheMoon,theextentoflargeimpactcratering(i.e.craterstoobig
tohavebeenfilledinbyerosionsincetheywereformed)servesasanage
indicatorfortheMartiansurface.Ageestimatesrangingfromfourbillionyears
forMars’ssouthernhighlandstoafewhundredmillionyearsintheyoungest
volcanicareaswereobtainedinthisway.
ThedetailedappearanceofMartianimpactcratersprovidesanimportant
pieceofinformationaboutconditionsjustbelowtheplanet’ssurface.Martian
cratersaresurroundedbyejecta(debrisformedasaresultofanimpact)that
looksquitedifferentfromitslunarcounterparts.Acomparisonofthe
CopernicuscraterontheMoonwiththe(fairlytypical)craterYutyonMars
demonstratesthedifferences.Theejectasurroundingthelunarcraterisjust
whatonewouldexpectfromanexplosionejectingalargevolumeofdust,soil,
andboulders.■However,theejectaonMarsgivesthedistinctimpressionofa
liquidthathassplashedorflowedoutofcrater.■Geologiststhinkthatthis
fluidizedejectacraterindicatesthatalayerofpermafrost,orwaterice,lies
justafewmetersunderthesurface.■Explosiveimpactsheatedandliquefiedthe
ice,resultinginthefluidappearanceoftheejecta.■
Q1Theword“enormous”inthepassageisclosestinmeaningto
A.Important
B.Extremelylarge
C.Highlyunusual
D.Active
Q2Accordingtoparagraph1,OlympusMonsdiffersfromvolcanoesonthe
TharsisbulgeinthatOlympusMons
A.Hasmorecomplexgeologicfeatures
B.Showslessimpactcratering
C.Istaller
D.Wasformedatalatertime
Q3Theword“distinctive”inthepassageisclosestinmeaningto
A.Deep
B.Complex
C.Characteristic
D.Ancient
Q4Accordingtoparagraphs1and2,whichofthefollowingisNOTtrueof
theshieldvolcanoesontheTharsisbulge?
A.Theyhavebroad,slopingsides.
B.TheyaresmallerthanthelargestvolcanoonMars.
C.Theyhavechannelsthatresemblethelavachannelsofvolcanoeson
Earth.
D.Theyareover25kilometerstall.
Q5Theword“roughly”inthepassageisclosestinmeaningto
A.Typically
B.Frequently
C.Actually
D.Approximately
Q6Inparagraph3,whydoestheauthorcompareMaxwellMonsonVenustothe
HawaiianshieldvolcanoesonEarth?
A.Tohelpexplaintherelationshipbetweensurfacegravityandvolcano
height
B.ToexplainwhyMars’ssurfacegravityisonly40percentofEarth’s
C.TopointoutdifferencesbetweenthesurfacegravityofEarthandthe
surfacegravityofVenus
D.Toarguethattherearemoresimilaritiesthandifferencesbetween
volcanoeson
differentplanetsParagraph3ismarkedwithanarrow>
Q7Whichofthesentencesbelowbestexpressestheessentialinformationin
thehighlightedsentenceinthepassage?
Incorrectchoiceschangethemeaningin
importantwaysorleaveoutessentialinformation.
A.Althoughdirectevidenceofrecenteruptionsislacking,scientists
believethatthesevolcanoeswereactiveasrecentlyas100millionyears
ago.
B.Scientistsestimatethatvolcanoesactivemorerecentlythan100years
agowillstillhaveextensiveimpactcrateringontheirslopes.
C.If,assomeevidencesuggests,thesevolcanoeseruptedasrecentlyas
100millionyearsago,theymaycontinuetobeintermittentlyactive.
D.Althoughthesevolcanoeswereactiveasrecentlyas100millionyears
ago,thereisnodirectevidenceofrecentorongoingeruptions.
Q8Theword“considerably”inthepassageisclosestinmeaningto
A.Frequently
B.Significantly
C.Clearly
D.Surprisingly
Q9Accordingtoparagraph4,whatisdemonstratedbythefactthatcraters
fillinmuchfasteronMarsthanontheMoon?
A.ErosionfrommeteoriticimpactstakesplacemorequicklyonMarsthanon
theMoon.
B.ThereismoredustonMarsthanontheMoon.
C.ThesurfaceofMarsisadrydesert.
D.WindisapowerfulerodingforceonMars.
Q10Inparagraph4,whydoestheauthorpointoutthatMarshasfewancient
cratersthatarelessthan5kilometersindiameter?
A.Toexplainwhyscientistsbelievethatthesurfacematterfilling
Martiancratersismostlydust
B.ToexplainwhyscientistsbelievethattheimpactcratersonMarswere
createdbymeteoroids
C.TosupporttheclaimthattheMartianatmosphereisanefficienterosive
agent
D.ToarguethatMarsexperiencedfewerancientimpactsthantheMoon
did
Q11Accordingtoparagraph5,whathavescientistsbeenabletodetermine
fromstudiesoflargeimpactcrateringonMars?
A.SomeMartianvolcanoesaremucholderthanwasoncethought.
B.TheageofMars’ssurfacecanvaryfromareatoarea.
C.Largeimpactcratersarenotreliableindicatorsofageinareaswith
highvolcanicactivity.
D.SomeareasoftheMartiansurfaceappeartobeolderthantheyactually
are.
Q12Accordingtoparagraph6,theejectaofMars’scraterYutydiffersfrom
theejectaoftheMoon’sCopernicuscraterinthattheejectaoftheYuty
crater
A.Hasnowbecomepartofapermafrostlayer
B.Containsalargevolumeofdust,soilandboulders
C.Suggeststhatliquidoncecameoutofthesurfaceatthecratersite
D.Wasthrownacomparativelylongdistancefromthecenterofthe
Q13Lookatthefoursquares【■】thatindicate
wherethefollowingsentencecouldbeaddedtothepassage.
ThissurfacefeaturehasledtospeculationaboutwhatmaylieunderMars’s
surface.
Wherewouldthesentencebestfit?
Clickonasquaretoaddthesentenceto
thepassage.
Q14Directions:
Anintroductorysentenceforabriefsummaryofthepassage
isprovidedbelow.CompletethesummarybyselectingtheTHREEanswerchoices
thatexpressthemostimportantideasinthepassage.Somesentencesdonot
belonginthesummarybecausetheyexpressideasthatarenotpresentedinthe
passageorareminorideasinthepassage.Thisquestionisworth2points.
Dragyouranswerchoicestothespaceswheretheybelong.Toremovean
answerchoice,clickonit.Toreviewthepassage,clickVIEWNEXT.
VolcanoesandimpactcratersaremajorfeaturesofMartiangeology.
A.PlatemotiononMars,onceconsideredtohaveplayednoroleinshaping
theplanet’ssurface,isnowseenasbeingdirectlyassociatedwiththeplanet’s
earliestvolcanoes.
B.Marshasshieldvolcanoes,someofwhichareextremelytallbecauseof
theplanet’slowsurfacegravity.
C.AlthoughtheerosivepoweroftheMartianatmosphereensuresthatMa
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