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TheSurfaceofMars

Paragraph1

ThesurfaceofMarsshowsawiderangeofgeologicfeatures,includinghugevolcanoes-thelargestknowninthesolarsystem-andextensiveimpactcratering.ThreeverylargevolcanoesarefoundontheTharsisbulge,anenormousgeologicareanearMars'sequator.NorthwestofTharsisisthelargestvolcanoofall:

OlympusMons,withaheightof25kilometersandmeasuringsome700kilometersindiameteratitsbase.ThethreelargevolcanoesontheTharsisbulgearealittlesmaller-a"mere"18kilometershigh.

Paragraph2

NoneofthesevolcanoeswasformedasaresultofcollisionsbetweenplatesoftheMartiancrust-thereisnoplatemotiononMars.Instead,theyareshieldvolcanoes-volcanoeswithbroad,slopingslidesformedbymoltenrock.AllfourshowdistinctivelavachannelsandotherflowfeaturessimilartothosefoundonshieldvolcanoesonEarth.ImagesoftheMartiansurfacerevealmanyhundredsofvolcanoes.MostofthelargestvolcanoesareassociatedwiththeTharsisbulge,butmanysmalleronesarefoundinthenorthernplains.

Paragraph3

ThegreatheightofMartianvolcanoesisadirectconsequenceoftheplanet'slowsurfacegravity.Aslavaflowsandspreadstoformashieldvolcano,thevolcano'seventualheightdependsonthenewmountain'sabilitytosupportitsownweight.Thelowerthegravity,thelessertheweightandthegreatertheheightofthemountain.ItisnoaccidentthatMaxwellMonsonVenusandtheHawaiianshieldvolcanoesonEarthrisetoaboutthesameheight（about10kilometers）abovetheirrespectivebases-EarthandVenushavesimilarsurfacegravity.Mars'ssurfacegravityisonly40percentthatofEarth,sovolcanoesriseroughly2.5timesashigh.AretheMartianshieldvolcanoesstillactive?

Scientistshavenodirectevidenceforrecentorongoingeruptions,butifthesevolcanoeswereactiveasrecentlyas100million,yearsago（anestimateofthetimeoflast"eruptionbasedontheextentofimpactcrateringontheirslopes）,someofthemmaystillbeatleastintermittentlyactive.Millionsofyears,though,maypassbetweeneruptions.

Paragraph4

AnotherprominentfeatureofMars'ssurfaceiscratering.TheMarinerspacecraftfoundthatthesurfaceofMars,aswellasthatofitstwomoons,ispittedwithimpactcratersformedbymeteoroidsfallinginfromspace.AsonourMoon,thesmallercratersareoftenfilledwithsurfacematter-mostlydust-confirmingthatMarsisadrydesertworld.However,Martiancratersgetfilledinconsiderablyfasterthantheirlunarcounterparts.OntheMoon,ancientcraterslessthan100metersacross（correspondingtodepthsofabout20meters）havebeenobliterated,primarilybymeteoriticerosion.OnMars,therearerelativelyfewcraterslessthan5kilometersindiameter.TheMartianatmosphereisanefficienterosiveagent,withMartianwindstransportingdustfromplacetoplaceanderasingsurfacefeaturesmuchfasterthanmeteoriticimpactsalonecanobliteratethem.

Paragraph5

AsontheMoon,theextentoflargeimpactcratering（i.e.craterstoobigtohavebeenfilledinbyerosionsincetheywereformed）servesasanageindicatorfortheMartiansurface.AgeestimatesrangingfromfourbillionyearsforMars'ssouthernhighlandstoafewhundredmillionyearsintheyoungestvolcanicareaswereobtainedinthisway.

Paragraph6

ThedetailedappearanceofMartianimpactcratersprovidesanimportantpieceofinformationaboutconditionsjustbelowtheplanet'ssurface.Martiancratersaresurroundedbyejecta（debrisformedasaresultofanimpact）thatlooksquitedifferentfromitslunarcounterparts.AcomparisonoftheCopernicuscraterontheMoonwiththe（fairlytypical）craterYutyonMarsdemonstratesthedifferences.Theejectasurroundingthelunarcraterisjustwhatonewouldexpectfromanexplosionejectingalargevolumeofdust,soil,andboulders.However,theejectaonMarsgivesthedistinctimpressionofaliquidthathassplashedorflowedoutofcrater.Geologiststhinkthatthisfluidizedejectacraterindicatesthatalayerofpermafrost,orwaterice,liesjustafewmetersunderthesurface.Explosiveimpactsheatedandliquefiedtheice,resultinginthefluidappearanceoftheejecta.

Paragraph1

ThesurfaceofMarsshowsawiderangeofgeologicfeatures,includinghugevolcanoes-thelargestknowninthesolarsystem-andextensiveimpactcratering.ThreeverylargevolcanoesarefoundontheTharsisbulge,anenormousgeologicareanearMars'sequator.NorthwestofTharsisisthelargestvolcanoofall:

OlympusMons,withaheightof25kilometersandmeasuringsome700kilometersindiameteratitsbase.ThethreelargevolcanoesontheTharsisbulgearealittlesmaller-a"mere"18kilometershigh.

1、Theword"enormous"Inthepassageisclosestinmeaningto

○Important

○Extremelylarge

○Highlyunusual

○Active

2、Accordingtoparagraph1,OlympusMonsdiffersfromvolcanoesontheTharsisbulgeinthatOlympus

Mons

○Hasmorecomplexgeologicfeatures

○Showslessimpactcratenng

○istaller

○Wasformedatalatertime

Paragraph2

NoneofthesevolcanoeswasformedasaresultofcollisionsbetweenplatesoftheMartiancrust-thereisnoplatemotiononMars.Instead,theyareshieldvolcanoes-volcanoeswithbroad,slopingslidesformedbymoltenrock.AllfourshowdistinctivelavachannelsandotherflowfeaturessimilartothosefoundonshieldvolcanoesonEarth.ImagesoftheMartiansurfacerevealmanyhundredsofvolcanoes.MostofthelargestvolcanoesareassociatedwiththeTharsisbulge,butmanysmalleronesarefoundinthenorthernplains.

3、Theword"distinctive”inthepassageisclosestinmeaningto

○Deep

○Complex

○Characteristic

○Ancient

4、Accordingtoparagraphs1and2,whichofthefollowingisNOTtrueoftheshieldvolcanoesontheTharsisbulge?

Theyhavebroad,slopingsides.

TheyaresmallerthanthelargestvolcanoonMars.

TheyhavechannelsthatresemblethelavachannelsofvolcanoesonEarth.

Theyareover25kilometerstall.

Paragraph3

ThegreatheightofMartianvolcanoesisadirectconsequenceoftheplanet'slowsurfacegravity.Aslavaflowsandspreadstoformashieldvolcano,thevolcano'seventualheightdependsonthenewmountain'sabilitytosupportitsownweight.Thelowerthegravity,thelessertheweightandthegreatertheheightofthemountain.ItisnoaccidentthatMaxwellMonsonVenusandtheHawaiianshieldvolcanoesonEarthrisetoaboutthesameheight（about10kilometers）abovetheirrespectivebases-EarthandVenushavesimilarsurfacegravity.Mars'ssurfacegravityisonly40percentthatofEarth,sovolcanoesriseroughly2.5timesashigh.AretheMartianshieldvolcanoesstillactive?

Scientistshavenodirectevidenceforrecentorongoingeruptions,butifthesevolcanoeswereactiveasrecentlyas100million,yearsago（anestimateofthetimeoflast"eruptionbasedontheextentofimpactcrateringontheirslopes）,someofthemmaystillbeatleastintermittentlyactive.Millionsofyears,though,maypassbetweeneruptions.

5、Theword"roughly"closestInmeaningto

Typically

Frequently

Actually

Approximately

6、Inparagraph3,whydoestheauthorcompareMaxwellMonsonVenustotheHawaiianshieldvolcanoesonEarth?

Tohelpexplaintherelationshipbetweensurfacegravityandvolcanoheight

ToexplainwhyMars'ssurfacegravityisonly40percentofEarth's

TopointoutdifferencesbetweenthesurfacegravityofEarthandthesurfacegravityofVenus

Toarguethattherearemoresimilaritiesthandifferencesbetweenvolcanoesondifferentplanets

7、Whichofthesentencesbelowbestexpressestheessentialinformationinthehighlightedsentenceinthepassage?

Incorrectchoiceschangethemeaninginimportantwaysorleaveoutessentialinformation.

Althoughdirectevidenceofrecenteruptionsislacking,scientistsbelievethatthesevolcanoeswereactiveasrecentlyas100millionyearsago.

Scientistsestimatethatvolcanoesactivemorerecentlythan100yearsagowillstillhaveextensiveimpactcrateringontheirslopes.

If,assomeevidencesuggests,thesevolcanoeseruptedasrecentlyas100millionyearsago,theymaycontinuetobeintermittentlyactive.

Althoughthesevolcanoeswereactiveasrecentlyas100millionyearsago,thereisnodirectevidenceofrecentorongoingeruptions.

Paragraph4

AnotherprominentfeatureofMars'ssurfaceiscratering.TheMarinerspacecraftfoundthatthesurfaceofMars,aswellasthatofitstwomoons,ispittedwithimpactcratersformedbymeteoroidsfallinginfromspace.AsonourMoon,thesmallercratersareoftenfilledwithsurfacematter-mostlydust-confirmingthatMarsisadrydesertworld.However,Martiancratersgetfilledinconsiderablyfasterthantheirlunarcounterparts.OntheMoon,ancientcraterslessthan100metersacross（correspondingtodepthsofabout20meters）havebeenobliterated,primarilybymeteoriticerosion.OnMars,therearerelativelyfewcraterslessthan5kilometersindiameter.TheMartianatmosphereisanefficienterosiveagent,withMartianwindstransportingdustfromplacetoplaceanderasingsurfacefeaturesmuchfasterthanmeteoriticimpactsalonecanobliteratethem.

8、Theword"considerably"inthepassageisclosestinmeaningto

Frequently

Significantly

Clearly

Surprisingly

9、Accordingtoparagraph4,whatisdemonstratedbythefactthatcratersfillinmuchfasteronMarsthanontheMoon?

ErosionfrommeteoriticimpactstakesplacemorequicklyonMarsthanontheMoon.

ThereismoredustonMarsthanontheMoon.

ThesurfaceofMarsisadrydesert.

WindisapowerfulerodingforceonMars.

10、Inthepapragraph4,whydoestheauthorpointoutthatMarshasfewancientcratersthatar