托福TPO阅读45文本.docx

托福TPO阅读45文本.docx

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托福TPO阅读45文本

托福TPO阅读45文本+题目+答案

1.MicroscopesTheBeringiaLandscape

Duringthepeakofthelasticeage,northeastAsia（Siberia）andAlaskawereconnectedbyabroadlandmasscalledtheBeringLandBridge.ThislandbridgeexistedbecausesomuchofEarth’swaterwasfrozeninthegreaticesheetsthatsealevelswereover100meterslowerthantheyaretoday.Between25,000and10,000yearsago,Siberia,theBeringLandBndge,andAlaskasharedmanyenvironmentalcharacteristics.Theseincludedacommonmammalianfaunaoflargemammals,acommonfloracomposedofbroadgrasslandsaswellaswind-sweptdunesandtundra,andacommonclimatewithcold,drywintersandsomewhatwannersummers.TherecognitionthatmanyaspectsofthemodemfloraandfaunawerepresentonbothsidesoftheBeringSeaasremnantsoftheice-agelandscapeledtothisregionbeingnamedBeringia.

ItisthroughBeringiathatsmallgroupsoflargemammalhunters,slowlyexpandingtheirhuntingterritories,eventuallycolonizedNorthandSouthAmerica.Onthisarchaeologistsgenerallyagree,butthatiswheretheagreementstopsOnebroadareaofdisagreementinexplainingthepeoplingoftheAmericasisthedomainofpaleoecologists,butitiscriticaltounderstandinghumanhistory:

whatwasBeringialike?

TheBeringianlandscapewasverydifferentfromwhatitistoday.■Broad,windsweptvalleys;glaciatedmountains;sparsevegetation;andlessmoisturecreatedaratherforbiddinglandmass.■Thislandmasssupportedherdsofnow-extinctspeciesofmammoth,bison,andhorseandsomewhatmodernversionsofcaribou,muskox,elk,andsaigaantelope.■Thesegrazerssupportedinturnanumberofimpressivecarnivores,includingthegiantshort-facedbear,thesaber-toothcat,andalargespeciesoflion.■

ThepresenceofmammalspeciesthatrequiregrasslandvegetationhasledArcticbiologistDaleGuthrietoarguethatwhilecoldanddry,theremusthavebeenbroadareasofdensevegetationtosupportherdsofmammoth,horse,andbison.Further,nearlyalloftheice-agefaunahadteeththatindicateanadaptationtograssesandsedges;theycouldnothavebeensupportedbyamodernfloraofmossesandlichens.Guthriehasalsodemonstratedthatthelandscapemusthavebeensubjecttointenseandcontinuouswinds,especiallyinwinter.Hemakesthisargumentbasedontheanatomy

ofhorseandbison,whichdonothavetheabilitytosearchforfoodthroughdeepsnowcover.Theyneedlandscapeswithstrongwindsthatremovethewintersnows,exposingthedrygrassesbeneath.Guthrieappliedtheterm“mammothsteppe"tocharacterizethislandscape.

Incontrast,PaulColinvauxhasofferedacounterargumentbasedontheanalysisofpolleninlakesedimentsdatingtothelasticeage.HefoundthattheamountofpollenrecoveredinthesesedimentsissolowthattheBeringianlandscapeduringthepeakofthelastglaciationwasmorelikelytohavebeenwhathetermeda"polardesert,"withlittleoronlysparsevegetation,innowaywasitpossiblethatthisregioncouldhavesupportedlargeherdsofmammalsandthus,humanhunters.Guthriehasarguedagainstthisviewbypointingoutthatradiocarbonanalysisofmammoth,horse,andbisonbonesfromBeringiandepositsrevealedthatthebonesdatetotheperiodofmostintenseglaciation.

Theargumentseemedtobeatastandstilluntilanumberofrecentstudiesresultedinaspectacularsuiteofnewfinds.Thefirstwasthediscoveryofa1,000-square-kilometerpreservedpatchofBeringianvegetationdatingtojustover17,000yearsago—thepeakofthelasticeageTheplantswerepreservedunderathickashfallfromavolcaniceruption.Investigationsoftheplantsfoundgrasses,sedges,mosses,andmanyothervarietiesinanearlycontinuouscover,aswaspredictedbyGuthrie.Butthisvegetationhadathinrootmatwithnosoilformation,demonstratingthattherewaslittlelong-termstabilityinplantcover,afindingsupportingsomeoftheargumentsofColinvaux.Amixtureofcontinuousbutthinvegetationsupportingherdsoflargemammalsisonethatseemsplausibleandrealisticwiththeavailabledata.

1.Theword"remnants"inthepassageisclosestinmeaning

Oremains

Oevidence

Oresults

Oreminders

2.Theword"domain"inthepassageisclosestinmeaningto

Ofieldofexpertise

Ochallenge

Ointerest

Oresponsibility

3.Accordingtoparagraph3,allofthefollowingaretrueoftheBeringianlandscapeEXCEPT.

OTherewaslittlevegetation.

OThemammalspeciesthereallsurvivedintomodernversions.

OTheclimatewasdrierthanitistoday.

OThereweremountainswithglaciers.

4.Thepurposeofparagraph3isto

Ocontrasttoday’sBeringianlandscapewithotherlandscapesintheAmericancontinent

OdescribetheBeringianlandscapeduringthelasticeage

OexplainwhysomanyBeringianspeciesbecameextinctduringthelasticeage

O