2025年托福阅读真题备考资料

2025年托福阅读真题备考资料Passage1TheEvolutionofC4PhotosynthesisPhotosynthesisisthebiologicalprocessbywhichplantsconvertlightenergyintochemicalenergy,fuelingthevastmajorityoflifeonEarth.ThemostcommonformofphotosynthesisisknownasC3photosynthesis,namedafterthethree-carboncompound(3-phosphoglycerate)producedintheCalvincycle,thefirststageofcarbonfixation.However,approximately3%ofplantspeciesutilizeadistinctmechanismcalledC4photosynthesis.Thisalternativepathwayevolvedindependentlyinover60differentlineagesofplants,suggestingitisahighlysuccessfuladaptationtospecificenvironmentalconditions,particularlythosecharacterizedbyhightemperatures,intensesunlight,andlimitedwateravailability.ThefundamentallimitationofC3photosynthesisliesinthenatureoftheenzymeresponsibleforcapturingcarbondioxide:ribulose-1,5-bisphosphatecarboxylase-oxygenase,commonlyknownasRuBisCO.WhileRuBisCOisessentialforfixingcarbon,itisnotoriouslyinefficient.Itcannotperfectlydistinguishbetweencarbondioxide(CO2)andoxygen(O2).Whenoxygenlevelsarehighrelativetocarbondioxide—aconditionoftenexacerbatedbyhot,dryweatherbecauseplantsclosetheirstomatatoconservewater,trappingO2andreleasingCO2insidetheleaf—RuBisCObindswithoxygeninstead.Thisprocess,calledphotorespiration,consumesenergyandreleasespreviouslyfixedcarbon,significantlyreducingtheplant'sphotosyntheticefficiencyandbiomassyield.C4plantscircumventtheinefficiencyofRuBisCOthroughasophisticatedanatomicalandbiochemical"CO2concentratingmechanism."UnlikeC3plants,wheretheentirephotosyntheticprocessoccursinasingletypeofcell(mesophyllcells),C4plantspossessauniqueKranzanatomy.Theyutilizetwodistincttypesofcells:mesophyllcellsandbundlesheathcells.Theprocessbeginsinthemesophyllcells,whereanenzymecalledPEPcarboxylasefixesatmosphericCO2intofour-carbonorganicacids(oxaloacetate,whichisquicklyconvertedtomalateoraspartate).PEPcarboxylasehasanextremelyhighaffinityforCO2anddoesnotreactwithoxygen,effectivelyeliminatingphotorespirationatthisinitialstage.Thesefour-carbonacidsarethentransportedintothebundlesheathcells,whichsurroundthevascularbundlesoftheleaf.Here,theacidsaredecarboxylated,releasingahighconcentrationofCO2incloseproximitytoRuBisCO.Becausethebundlesheathcellsareoftenimpermeabletogases,thislocalizedCO2concentrationcreatesanenvironmentwhereRuBisCOcanfunctionatmaximumefficiency,saturatingtheenzymewithCO2andminimizingthechanceofoxygenbinding.AftercarbonfixationbyRuBisCOintheCalvincycle,theremainingthree-carbonproductistransportedbacktothemesophyllcellstoregeneratethePEPmolecule,completingthecycle.TheevolutionofC4photosynthesisrequiredsignificantchangesinleafanatomyandgeneexpression.Despitethecomplexity,thistraitemergedconvergentlyindiversefamilies,includinggrasses(Poaceae),sedges(Cyperaceae),andamaranths(Amaranthaceae).ThedrivingforcebehindthisconvergenceiswidelybelievedtobethedeclineinatmosphericCO2levelsduringtheOligoceneandMioceneepochs,roughly30to5millionyearsago.AsglobalCO2concentrationsdropped,theratioofCO2toO2intheatmosphereshifted,makingphotorespirationmorefrequentandcostlyforC3plants.Inthislow-CO2atmosphere,theenergeticcostofmaintainingtheC4pumpwasoutweighedbythebenefitsofreducedphotorespiration,givingC4plantsacompetitiveadvantageinhot,arid,andopenhabitats.Today,C4plantsdominatetropicalandsubtropicalgrasslandsandsavannas.Manyoftheworld'smostimportantcrops,includingmaize(corn),sugarcane,sorghum,andmillet,areC4plants.Theyareresponsibleforabout20-30%ofglobalterrestrialgrossprimaryproductivitydespitebeingasmallminorityofplantspecies.Theirhighwater-useefficiencyandnitrogen-useefficiencymakethemparticularlywell-suitedforagricultureinregionsfacingwaterscarcityandpoorsoilquality.UnderstandingthegeneticandphysiologicalbasisofC4photosynthesisremainsamajorgoalinplantbiology,withongoingresearchexploringthepossibilityofengineeringC4mechanismsintoC3cropslikericeandwheattoenhancetheiryieldandresilienceinthefaceofclimatechange.Questions1-101.Theword"distinct"inthepassageisclosestinmeaningtoA.separateB.distinctC.clearD.distinctive2.Accordingtoparagraph2,whydoesphotorespirationoccurinC3plants?A.RuBisCObindswithoxygeninsteadofcarbondioxidewhenoxygenlevelsarehighinsidetheleaf.B.TheCalvincycleproducestoomuch3-phosphoglycerate,whichinhibitsphotosynthesis.C.Hightemperaturescausethestomatatoopen,releasingtoomuchcarbondioxide.D.C3plantslackthenecessaryenzymestoprocesscarbondioxideinhotweather.3.WhichofthefollowingstatementsaboutPEPcarboxylaseissupportedbyparagraph3?A.ItistheprimaryenzymeusedintheCalvincyclewithinbundlesheathcells.B.ItislessefficientthanRuBisCOatfixingcarbondioxidebutdoesnotreactwithoxygen.C.Itfixescarbondioxideintofour-carbonacidsinthemesophyllcells.D.Ittransportsmalateandaspartatetothevascularbundles.4.Theword"impermeable"inthepassageisclosestinmeaningtoA.permeableB.impenetrableC.transparentD.solid5.Accordingtoparagraph4,howdoC4plantsensurethatRuBisCOfunctionsefficiently?A.ByincreasingtheamountofRuBisCOenzymesinthemesophyllcells.B.Bykeepingthestomataopentoallowconstantgasexchange.C.BycreatingahighconcentrationofCO2aroundRuBisCOinthebundlesheathcells.D.Byconvertingoxygenintocarbondioxidebeforeitreachestheenzyme.6.Thephrase"outweighedby"inthepassageisclosestinmeaningtoA.exceededbyB.balancedbyC.compensatedforD.dominatedby7.WhydoestheauthormentiontheOligoceneandMioceneepochsinparagraph5?A.TosuggestthatC4plantsaretheoldestformofplantlifeonEarth.B.Toexplainthegeologicalconditionsthatledtotheformationofgrasslands.C.ToidentifythehistoricalperiodwhenatmosphericCO2levelsdropped,favoringC4evolution.D.Tocontrasttheclimateofthepastwiththecurrentclimatechangecrisis.8.Whichofthesentencesbelowbestexpressestheessentialinformationinthefollowingsentence?"AsglobalCO2concentrationsdropped,theratioofCO2toO2intheatmosphereshifted,makingphotorespirationmorefrequentandcostlyforC3plants."A.C3plantsbecamemoreexpensivetogrowasCO2levelsdroppedbecausetheyrequiredmoreoxygen.B.ThedropinCO2levelsmadephotorespirationhappenmoreoften,whichwasadisadvantageforC3plants.C.WhenCO2levelsdropped,C3plantsevolvedtouseoxygenmoreefficientlythancarbondioxide.D.TheshiftingratioofgasesintheatmospherecausedC3plantstobecomethedominantspecies.9.Lookatthefourletters[A],[B],[C],[D]thatindicatewherethefollowingsentencecouldbeaddedtothepassage."Consequently,theseplantsloselesswaterperunitofcarbonfixedcomparedtotheirC3counterparts."Wherewouldthesentencebestfit?A.[A]Today,C4plantsdominatetropicalandsubtropicalgrasslandsandsavannas.B.[B]Manyoftheworld'smostimportantcrops,includingmaize(corn),sugarcane,sorghum,andmillet,areC4plants.C.[C]Theyareresponsibleforabout20-30%ofglobalterrestrialgrossprimaryproductivitydespitebeingasmallminorityofplantspecies.D.[D]Theirhighwater-useefficiencyandnitrogen-useefficiencymakethemparticularlywell-suitedforagricultureinregionsfacingwaterscarcityandpoorsoilquality.10.Directions:Anintroductorysentenceforabriefsummaryofthepassageisprovidedbelow.CompletethesummarybyselectingtheTHREEanswerchoicesthatexpressthemostimportantideasinthepassage.Somesentencesdonotbelonginthesummarybecausetheyexpressideasthatarenotpresentedinthepassageorareminorideasinthepassage.C4photosynthesisisanevolutionaryadaptationthatallowscertainplantstothriveinenvironmentswherestandardC3photosynthesisisinefficient._______________________________________________________________________A.C3photosynthesisishinderedbyphotorespiration,aprocesswhereRuBisCObindswithoxygen,reducingefficiencyinhot,dryconditions.B.C4plantsutilizeauniqueanatomyinvolvingmesophyllandbundlesheathcellstoconcentrateCO2aroundRuBisCO.C.TheevolutionofC4photosynthesiswasdrivenbyahistoricaldeclineinatmosphericCO2levels,makingC4plantsmorecompetitive.D.AllplantsthatliveintropicalregionsutilizeC4photosynthesisbecauseitrequiresmoresunlightthanC3photosynthesis.E.RuBisCOisanenzymefoundonlyinC3plantsandisresponsibleforcapturingnitrogenfromthesoil.F.ScientistsarecurrentlyattemptingtotransferC4characteristicstomajorC3cropstoimprovefoodsecurity.Passage2TheSocio-EconomicImpactofthePrintingPressTheinventionofthemovabletypeprintingpressbyJohannesGutenbergaround1440iswidelyregardedasoneofthemostpivotaleventsinhumanhistory,oftenrankedalongsidetheinventionofthewheelorthediscoveryoffire.WhilethetechnologyofwoodblockprintinghadexistedinChinaandKoreacenturiesprior,Gutenberg'spress,combinedwithhisdevelopmentofadurableoil-basedinkandamovablemetaltypealloy,revolutionizedtheproductionofbooksinEurope.Thistechnologicalshiftdidnotmerelyalterthemechanicsofbookproduction;itfundamentallytransformedthesocio-economiclandscapeoftheRenaissance,actingasacatalystforthespreadofliteracy,thestandardizationoflanguages,andthedemocratizationofknowledge.Beforetheadventoftheprintingpress,bookswerepainstakinglycopiedbyhand,typicallybyscribesinmonasteries.Thislabor-intensiveprocessmadebooksexorbitantlyexpensiveluxuryitems,accessibleonlytotheclergy,thearistocracy,andextremelywealthymerchants.Asinglemanuscriptcouldtakemonthsorevenyearstocomplete,andtheoutputofascriptoriumwaslimited.Consequently,thevastmajorityofthepopulationwasilliterate,andknowledgewastightlycontrolledbytheChurch.Theprintingpressshatteredthismonopoly.Bymechanizingproduction,Gutenbergandhissuccessorsreducedthetimeandcostofcreatingabookbyordersofmagnitude.Withinafewdecades,thepriceofbooksdroppedsignificantly,allowingfortheemergenceofaliteratemiddleclassandtheestablishmentofpublicandprivatelibraries.Theeconomicimplicationsoftheprintingpressextendedfarbeyondthebooktrade.Thepresswasthefirst"massproduction"industryinhistory.Itcreatedademandforpaper,whichreplacedtheexpensiveparchment(animalskin)usedformanuscripts.Thisspurredthegrowthofpapermills,whichwereoftensituatednearwatersourcestopowertheirmachinery.Furthermore,thepressrequiredaskilledlaborforceoftypefounders,compositors,andprinters,leadingtothecreationofnewguildsandaspecializedworkforce.ThespreadofprintingpressesacrossmajorEuropeancities—Venice,Paris,London,andAntwerp—facilitatedthegrowthofapan-Europeanbookmarket.Merchantsandtradersbegantoexchangebooksalongsidespicesandtextiles,turningknowledgeintoacommoditythatcouldbetradedacrossborders.Oneofthemostprofoundeffectsoftheprintingpresswasitsroleinthestandardizationofvernacularlanguages.PriortoGutenberg,Latinwasthelinguafrancaoftheeducatedelite,whileregionallanguageslikeEnglish,French,andGermanexistedinamultitudeofdialectswithinconsistentspellingsandgrammars.Asprinterssoughttomaximizetheirmarket,theybeganpublishinginthevernaculartoreachawideraudience.However,tomaketextscomprehensibleacrossdifferentregions,printershadtostandardizespellingandgrammar.Forinstance,WilliamCaxton,whobroughttheprintingpresstoEngland,isoftencreditedwithstandardizingEnglishthroughhisprintingchoices.Thisprocessinadvertentlystrengthenednationalidentitiesandlaidthegroundworkforthemodernnation-state.Theprintingpressalsoplayedacriticalroleinthereligiousupheavalsofthe16thcentury,mostnotablytheProtestantReformation.In1517,MartinLuthernailedhisNinety-fiveThesestothedoorofachurchinWittenberg.Whilethiswasatraditionalactofacademicdisputation,theprintingpressensuredthatLuther'sideaswerenotconfinedtolocalacademiccircles.PamphletsandbroadsidescontaininghiscriticismsoftheCatholicChurchwereprintedinthethousandsanddisseminatedrapidlythroughoutGermanyandbeyond.TheChurch'sabilitytosuppressheresy,whichreliedoncontrollingtheflowofinformation,wasrenderedobsoletebythespeedandvolumeofprint.TheresultingreligiouswarsandthefragmentationofChristendomwere,inmanyways,directconsequencesofthenewinformationageusheredinbythepress.However,thetransitiontoprintwasnotwithoutitschallenges.The"informationexplosion"ledtoanxietyamongintellectualsregardingthereliabilityoftexts.Withsomanybooksincirculation,distinguishingbetweenauthoritativeworksanderroneousorplagiarizedtextsbecamedifficult.Thisledtothedevelopmentofnewscholarlypractices,suchasfootnotes,bibliographies,andtitlepages,whichhelpedreadersnavigatethegrowingseaofinformation.Despitetheseinitialhurdles,theprintingpressestablishedarobustfoundationfortheScientificRevolutionandtheEnlightenment,providingareliablemediumforscientistsandphilosopherstosharedataandcritiquetheworkoftheirpeers.Questions11-2011.Theword"pivotal"inthepassageisclosestinmeaningtoA.centralB.trivialC.historicalD.ancient12.Accordingtoparagraph1,howdidGutenberg'spressdifferfromearlierprintingtechnologiesinEastAsia?A.Itwasthefirstpresstouseink.B.Itutilizedmovablemetaltypeandoil-basedinksuitableforEuropeanmaterials.C.Itwasentirelymechanical,whereasAsianpressesweremanual.D.ItwasinventedspecificallyforprintingtheBible.13.Whydoestheauthormentionscribesinmonasteriesinparagraph2?A.Tohighlighttheartisticskillinvolvedinhandwrittenmanuscripts.B.Toexplainwhybookswererareandexpensivebeforetheprintingpress.C.Tocontrastthespeedofmonasticlaborwiththatofmodernfactories.D.Toshowthattheclergyweretheonlypeoplewhocouldreadbeforethe15thcentury.14.Theword"exorbitantly"inthepassageisclosestinmeaningtoA.moderatelyB.slightlyC.excessivelyD.reasonably15.WhichofthefollowingisNOTmentionedinparagraph3asaneconomiceffectoftheprintingpress?A.Theincreaseddemandforpaperledtothegrowthofpapermills.B.Thecreationofspecializedjobsintheprintingindustry.C.Thedeclineoftheagriculturalsectorduetolaborshortages.D.Thedevelopmentofatrans-Europeanbooktrade.16.Accordingtoparagraph4,howdidtheprintingpressaffectvernacularlanguages?A.ItcausedthedeclineofLatinasalanguageofscholarship.B.Itencouragedprinterstostandardizespellingandgrammartoreachwideraudiences.C.Itmaderegionaldialectsdisappearcompletely.D.Itpreventedtheformationofnationalidentities.17.Theword"disseminated"inthepassageisclosestinmeaningtoA.discussedB.suppressedC.spreadD.written18.Whatcanbeinferredfromparagraph5abouttheCatholicChurchbeforetheprintingpress?A.ItactivelysupportedthetranslationoftheBibleintovernacularlanguages.B.Ithadeffectivemechanismstocontrolthespreadofinformation.C.ItwasunawareofMartinLuther'scriticismsuntilaftertheReformationbegan.D.ItownedalltheprintingpressesinEurope.19.Accordingtoparagraph6,whydidscholarsdevelopfootnotesandbibliographies?A.Toaddartisticflairtotheirpublications.B.Tocomplywithgovernmentregulationsonprinting.C.Tohelpreadersverifythereliabilityoftheincreasingnumberoftexts.D.Tocriticizetheworkoftheirpeersinamoreformalmanner.20.Directions:Anintroductorysentenceforabriefsummaryofthepassageisprovidedbelow.CompletethesummarybyselectingtheTHREEanswerchoicesthatexpressthemostimportantideasinthepassage.Somesentencesdonotbelonginthesummarybecausetheyexpressideasthatarenotpresentedinthepassageorareminorideasinthepassage.TheinventionoftheprintingpressbyJohannesGutenberghadprofoundandlastingeffectsonEuropeansociety,economy,andreligion._______________________________________________________________________A.Theprintingpressmadebookscheaperandmoreaccessible,breakingtheChurch'smonopolyonknowledge.B.Gutenberg'sinventionwasbasedentirelyonwoodblockprintingtechniquesimportedfromChina.C.Theprintingindustrystimulatedtheeconomybycreatingjobsandincreasingthedemandforpaper.D.Thestandardizationofvernacularlanguagesthroughprintingcontributedtotheriseofnationalidentities.E.TheprintingpresshelpedMartinLutherspreadhisideas,contributingtotheProtestantReformation.F.Theprimarypurposeoftheprintingpresswastoprintscientifictextbooksforuniversities.Passage3GlacialCyclesandMilankovitchCyclesForoveracentury,geologistsandclimatologistshavesoughttounderstandthedrivingforcesbehindthecyclicaladvancesandretreatsofglaciers,knownasglacial-interglacialcycles.TheEarthhasexperiencednumerousiceagesinitshistory,themostrecentofwhichbeganapproximately2.6millionyearsagoduringthePleistoceneepoch.Withinthisepoch,therehavebeencyclesofcoldperiods(glacials)andwarmperiods(interglacials),occurringroughlyevery100,000years.Whilevariousfactorscontributetoclimatechange,themostwidelyacceptedexplanationforthetimingofthesecyclesistheMilankovitchtheory,proposedbySerbianastronomerMilutinMilankovitchintheearly20thcentury.MilankovitchtheorypositsthatcyclicalchangesintheEarth'sorbitalgeometryandaxialorientationaffectthedistributionandintensityofsolarradiation(insolation)receivedbytheEarth'ssurface.Theseorbitalvariationsarenotrandom;theyoperateonpredictabletimescalesandareknownasMilankovitchcycles.Therearethreeprimarycomponentsofthesecycles:eccentricity,obliquity,andprecession.Thecollectiveeffectofthesecyclesalterstheamountandseasonaltimingofsunlightreachinghighlatitudes,whicharecriticalforthegrowthanddecayofcontinentalicesheets.Thefirstcomponent,eccentricity,referstotheshapeoftheEarth'sorbitaroundtheSun.Theorbitchangesfrombeingnearlycirculartoslightlyellipticaloveracycleofapproximately100,000years.Whentheorbitismoreelliptical,theEarth-Sundistancevariesmoresignificantlythroughouttheyear.However,thechangeintotalsolarradiationreceivedbytheEarthannuallyduetoeccentricityisverysmall.Thecriticalfactoristhepositionoftheseasonsrelativetotheperihelion(thepointinorbitclosesttotheSun)andaphelion(thepointfarthestfromtheSun).Thisdetermineswhetherahemisphereexperiencesasummernearperihelion(warmersummer)ornearaphelion(coolersummer).Thesecondcomponent,obliquity,isthetiltoftheEarth'saxisrelativetotheplaneofitsorbit.Theangleoftiltvariesbetween22.1°and24.5°overaperiodofabout41,000years.Thecurrenttiltisapproximately23.5°.Thedegreeoftiltiscrucialbecauseitdeterminestheintensityoftheseasons.Agreatertiltresultsinmoreextremeseasons:summersarehotter,andwintersarecolder.Conversely,asmallertiltleadstomilderseasons.Forglacialcycles,ahighertiltcantheoreticallypromotesummermelting,preventingiceaccumulation,whilealowertiltmightresultincoolersummersthatallowicetopersistthroughthemeltseason.Thethirdcomponent,precession,isthewobbleoftheEarth'saxisonitsaxis,similartothespinningofatop.Thiswobblecausesthetimingofthesolsticesandequinoxestoshiftslowlyoveracycleofroughly23,000years.PrecessiondetermineswhethertheNorthernHemispherepointstowardtheSunatperihelionoraphelion.IftheNorthernHemisphereistiltedtowardtheSunwhentheEarthisclosesttoit(perihelion),itreceivessignificantlymoreinsolationduringsummer.IfitistiltedtowardtheSunataphelion(whentheEarthisfarthestaway),thesummerinsolationisreduced.ThisvariationisparticularlyimportantfortheNorthernHemisphere,whichholdsthemajorityoftheEarth'slandmassandistheprimarysiteoflargeicesheetformation.Theinteractionofthesethreecyclescreatesacomplexpatternofinsolationathighnorthernlatitudes.The"100,000-yearproblem"isanoteddiscrepancyinpaleoclimatology.WhileMilankovitchtheorypredictsthatthe41,000-yearobliquitycycleshoulddominateglacialrhythms,geologicalrecordsfromthepastmillionyearsshowthatthe100,000-yeareccentricitycycleisdominant.Severalhypothesesattempttoexplainthis,includingtheideathaticesheetstakealongtimetobuildupanddisintegrate,introducingalagintheclimatesystem,orthattheclimatesystemisnon-linearandrespondsdifferentlywhenicesheetsreachacertainsize.Furthermore,theclimatesysteminvolvesinternalfeedbackmechanismsthatamplifytherelativelyweakforcingfromorbitalchanges.Themostsignificantoftheseistheice-albedofeedback.Iceandsnowhaveahighalbedo,meaningtheyreflectmostincomingsolarradiation.Asicesheetsgrowduringaglacialperiod,moresunlightisreflectedbackintospace,coolingtheplanetfurtherandallowingmoreicetogrow.Conversely,duringaninterglacialperiod,icemelts,revealingdarkerlandoroceansurfacesthatabsorbmoreheat,leadingtofurtherwarmingandmelting.Otherfeedbacksinvolvechangesingreenhousegasconcentrations(suchasCO2andmethane)recordedinicecores,whichcorrelatecloselywithtemperaturechanges.Insummary,whileMilankovitchcyclesprovidethe"pacemaker"fortheiceagesbymodulatingtheamountofsolarenergyreachingtheEarth,itistheEarth'sinternalfeedbackmechanismsthatdeterminethemagnitudeoftheclimaticresponse.Themathematicalrelationshipcanbeconceptuallyrepresentedbythebalanceofincomingandoutgoingradiation.ThechangeintemperatureΔTcanbemodeledasafunctionofthechangeinsolarradiationΔSandthefeedbackfactorλ,whereQuestions21-3021.Theword"posits"inthepassageisclosestinmeaningtoA.observesB.suggestsC.deniesD.calculates22.Accordingtoparagraph2,whatistheprimaryresultofMilankovitchcycles?A.TheychangethetotalamountofsolarradiationreachingtheEarthsignificantly.B.Theyalterthedistributionandseasonaltimingofsolarradiation,particularlyathighlatitudes.C.TheycauserandomfluctuationsintheEarth'smagneticfield.D.Theyareresponsibleforthedailycycleofdayandnight.23.Theword"eccentricity"inthepassagereferstoA.thetiltoftheEarth'saxis.B.thewobbleoftheEarth'saxis.C.theshapeoftheEarth'sorbitaroundtheSun.D.theintensityoftheseasons.24.Accordingtoparagraph4,howdoesobliquityaffecttheclimate?A.ItchangesthedistancebetweentheEarthandtheSun.B.Itdeterminesthelengthofthecalendaryear.C.Itinfluencestheseverityoftheseasons;agreatertiltcausesmoreextremeseasons.D.Itcausestheequinoxestoshiftovertime.25.WhydoestheauthorfocusontheNorthernHemisphereinparagraph5?A.BecausetheSouthernHemisphereismostlyoceananddoesnotformlargeicesheets.B.BecauseprecessiononlyaffectstheNorthernHemisphere.C.BecausethemajorityoftheEarth'slandmass,whereicesheetsform,islocatedthere.D.BecausetheSouthernHemisphereisalwaystiltedawayfromtheSun.26.Whatisthe"100,000-yearproblem"mentionedinparagraph6?A.Thegeologicalrecordshowsa100,000-yearcycle,butMilankovitchtheorypredictsthe41,000-yearcycleshouldbedominant.B.Scientistscannotexplainwhyiceageslastexactly100,000years.C.TheEarth'sorbitchangesshapeevery100,000years,buttheclimatedoesnotrespond.D.Theprecessioncycleis23,000years,whichdoesnotdivideevenlyinto100,000years.27.Theword"amplify"inthepassageisclosestinmeaningtoA.reduceB.magnifyC.initiateD.measure28.Accordingtoparagraph7,howdoestheice-albedofeedbackwork?A.Icereflectssunlight,causingcoolingandmoreicegrowth;meltingiceabsorbsheat,causingwarmingandmoremelting.B.Iceabsorbsheat,whichwarmstheatmosphereandmeltstheice.C.Albedoisameasureofgreenhousegasesintheatmosphere.D.Thefeedbackmechanismpreventsicesheetsfromgrowingtoolarge.29.WhichofthefollowingcanbeinferredabouttherelationshipbetweenMilankovitchcyclesandiceages?A.Milankovitchcyclesarethesolecauseoficeages;withoutthem,theEarthwouldneverfreeze.B.Thecyclesprovidethetimingforiceages,butfeedbacksdeterminehowseverethetemperaturechangesbecome.C.Thecyclesaretooweaktoaffecttheclimatewithouttheadditionofhuman-madegreenhousegases.D.The100,000-yearcycleisthemostimportantcyclebecauseitchangestheEarth'stiltthemost.30.Directions:Anintroductorysentenceforabriefsummaryofthepassageisprovidedbelow.CompletethesummarybyselectingtheTHREEanswerchoicesthatexpressthemostimportantideasinthepassage.Somesentencesdonotbelonginthesummarybecausetheyexpressideasthatarenotpresentedinthepassageorareminorideasinthepassage.Milankovitchtheoryexplainsthetimingofglacial-interglacialcyclesthroughchangesintheEarth'sorbitandorientation._______________________________________________________________________A.Thethreemaincyclesareeccentricity,obliquity,andprecession,whichaffectinsolationatdifferenttimescales.B.TheNorthernHemisphereistheprimaryfocusbecauseitcontainsthelandnecessaryforlargeicesheetformation.C.The"100,000-yearproblem"suggeststhatMilankovitch'scalculationswerecompletelyincorrect.D.Internalfeedbackmechanismslikeice-albedoandgreenhousegasesamplifytheinitialorbitalchanges.E.GlacialcyclesareprimarilycausedbychangesintheEarth'smagneticfield.F.Theinteractionbetweenorbitalforcingandclimatefeedbackshelpsscienti