625托福阅读真题.docx

625托福阅读真题.docx

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625托福阅读真题

CCDAC,BABCD,ABD,245

TheOriginofCoralReefs

Coralreefsarenaturalstructuresformedfromdepositsofthecalciumcarbonatesecretionsofcoral,amarineanimalthatlivesincolonies.Ingeneral,coralreefsaregroupedintooneofthreecategories,atolls,barrierreefs,andfringingreefs.Atollsareusuallyeasilydistinguishedbecausetheyaremodifiedhorseshoe-shapedreefsthatriseoutofverydeepwaterfarfromlandandenclosealagoon（abodyofcertainwatersurroundedbyacoralreef）.Withfewexceptions,atollsarefoundonlyintheIndo-Pacificarea.Barrierreefsandfringingreefs,ontheotherhand,tendtogradeintoeachotherandarenotreadilyseparable.Somescientistswouldprefertogroupthemintoasinglecategory.Bothtypesoccuradjacenttoalandmass,withabarrierreefbeingseparatedfromthelandmassbyagreaterdistanceanddeeperwaterchannelthanthefringingreef.Fringingreefsandbarrierreefsarecommonthroughoutthecoralreefzonesinalloceans.

Differenttypesofreefsandreefsindifferentoceansmayhavediverseoriginsandhistories.Thegreatestinterestintheoriginofreefshascenteredonatolls.Formanyyears,humansspeculatedastohowsuchreefscoulddevelopinsuchdeepwater,milesfromthenearestemergentland.Thisinterestwasheightenedwhenitwasdiscoveredthatreefcoralscoldnotlivedeeperthan50-70meters.Thisledtothedevelopmentofseveraltheoriesconcerningtheoriginofatolls.Onlyoneneedbediscussedhere——the………………growontheshoresofnewlyformedvolcanicislandsthathavepushedtothesurfacefromdeepwater.Theseislandsoftenbegintosubside,andifthesubsidenceisnottoofast,reefgrowthwillkeepupwiththesubsidence.Thereefgrowthwillthenformabarrierreefand,ultimately,anatollastheislanddisappearsbeneaththesea.Whentheislandhasdisappeared,coralscontinuetogrowontheoutsideandkeepthereefatthesurface.Ontheinside,wheretheislandusedtobe,quietwaterconditionsandhighsedimentationprevail.Theseconditionspreventcontinuedvigorouscoralgrowth,hence,alagoondevelops.Thistheorylinksallthreereeftypesintoevolutionarysequence,butisnotanexplanationforallfringingandbarrierreeftypes.

Sincethecurrentsurfacefeaturesofatollsgivenoevidenceofavolcanicbase,intheyearsafterthedevelopmentofDarwin’stheoryotherexplanationswereoffered,andthewholeconceptoftheoriginofatollsbecameembroiledinthecontroversyovertheoriginofcoralreefs.IfDarwin’stheorywascorrect,itmustbeassumedthatdrillingdownthroughthecurrentatollreefswouldyieldlayerafterlayerofreeflimestoneuntil,finally,volcanicrockwouldbeencountered.Theabilitytodrilltothebaseofatollreefsandresolvedtheproblemhadtowaituntilthemid-twentiethcenturyin1953.LaddandothergeologistsreportedboringsatEriwetokatollintheMarshallIslandsthatpenetrated1,283metersofreeflimestoneandthenhitvolcanicrock.ThiswastheevidencethatDarwin’stheorywassubstantiallycorrect.Thecorrectnessofthistheoryhasbeenstrengthenedbythediscoveryofflat-toppedmountainsorguyotsthat,atpresent,havetheirtopsmanyhundredsorthousandsofmetersbelowtheoceansurface,buthaveontheirsurfacetheremainsofshallowwatercorals.Evidently,thesemountainssanktoofastforreefgrowthtokeepabovetheoceansurface.

Althoughthesubsidencetheorylinksallthreereeftypesinasuccessionalsequence,notallbarrierreefsandfringingreefscanbeexplainedbythismechanism.Indeed,thereasonsbarrierandfringingreeftypesoccuraroundcontinentalmarginsandhighnon-volcanicislandsaresimplythattheseareasoffersuitableenvironmentalconditionsforthegrowthofreefsandasuitablesubstrate（surface）onwhichtobegingrowth.TheextensivereefsaroundtheIndonesianIslands,thePhilippines,NewGuinea,FijiandmostoftheCaribbeanIslandsaretherebecauseasuitablesubstrateinshallowwaterexistedonwhichtheycouldinitiategrowth.Innoneoftheseareasarelargelandareassubsiding,notwillthesereefsultimatelybecomeatolls.

Paragraph1

Coralreefsarenaturalstructuresformedfromdepositsofthecalciumcarbonatesecretionsofcoral,amarineanimalthatlivesincolonies.Ingeneral,coralreefsaregroupedintooneofthreecategories,atolls,barrierreefs,andfringingreefs.Atollsareusuallyeasilydistinguishedbecausetheyaremodifiedhorseshoe-shapedreefsthatriseoutofverydeepwaterfarfromlandandenclosealagoon（abodyofcertainwatersurroundedbyacoralreef）.Withfewexceptions,atollsarefoundonlyintheIndo-Pacificarea.Barrierreefsandfringingreefs,ontheotherhand,tendtogradeintoeachotherandarenotreadilyseparable.Somescientistswouldprefertogroupthemintoasinglecategory.Bothtypesoccuradjacenttoalandmass,withabarrierreefbeingseparatedfromthelandmassbyagreaterdistanceanddeeperwaterchannelthanthefringingreef.Fringingreefsandbarrierreefsarecommonthroughoutthecoralreefzonesinalloceans.

1.Accordingtoparagraph1,allofthefollowingaretrueofatollsEXCEPT

¡MostatollsoccurintheIndo-Pacificarea.

¡Atollsoccuronlyinverydeepwaters.

¡Atollsaremorecommonthanothertypesofreefs.

¡Atollsoccurfarfromalandmass.

2.Accordingtoparagraph1,fringingreefsandbarrierreefscanbeidentifiedby

¡theirsimilaritiestoatolls

¡theirorganizationintogroupsofseparableparts

¡theirdistancefromthenearestlandmass

¡whetherornottheyenclosealagoon

Paragraph2

Differenttypesofreefsandreefsindifferentoceansmayhavediverseoriginsandhistories.Thegreatestinterestintheoriginofreefshascenteredonatolls.Formanyyears,humansspeculatedastohowsuchreefscoulddevelopinsuchdeepwater,milesfromthenearestemergentland.Thisinterestwasheightenedwhenitwasdiscoveredthatreefcoralscoldnotlivedeeperthan50-70meters.Thisledtothedevelopmentofseveraltheoriesconcerningtheoriginofatolls.Onlyoneneedbediscussedhere——the………………growontheshoresofnewlyformedvolcanicislandsthathavepushedtothesurfacefromdeepwater.Theseislandsoftenbegintosubside,andifthesubsidenceisnottoofast,reefgrowthwillkeepupwiththesubsidence.Thereefgrowthwillthenformabarrierreefand,ultimately,anatollastheislanddisappearsbeneaththesea.Whentheislandhasdisappeared,coralscontinuetogrowontheoutsideandkeepthereefatthesurface.Ontheinside,wheretheislandusedtobe,quietwaterconditionsandhighsedimentationprevail.Theseconditionspreventcontinuedvigorouscoralgrowth,hence,alagoondevelops.Thistheorylinksallthreereeftypesintoevolutionarysequence,butisnotanexplanationforallfringingandbarrierreeftypes.

3.Thephrase“washeightened”inthepassageisclosestinmeaningto

¡developed

¡varied

¡continued

¡increased

4.Theword“prevail”inthepassageisclosetinmeaningto

¡dominate

¡combine

¡spread

¡compete

5.Whichofthefollowingcanbeinferredfromparagraph2asthereasonthattheoriginofatollshasgeneratedmoreinterestthanhastheoriginofothertypesofreefs?

¡Mostreefshaveapredictableshape,butatollsdonot.

¡Atollsappeartoformmorerapidlythanotherkindsofreefs.

¡Theanimalsthatformcoralreefscannotliveinwaterbelow70meters,butatollsonlyforminverydeepwater.

¡Atollshavemorediverseoriginsandhistoriesthanothertypesofreefs.

6.Accordingtoparagraph2,Darwin’ssubsidencetheoryprovidedananswertoeachofthefollowingquestionsEXCEPT

¡Howdoesalagoondevelop?

¡Whydovolcanicislandssubside?

¡Howdoesafringingreefbecomeabarrierreef?

¡Whathappenstocoralgrowthwhenavolcanicislandsubsidesslowly?

7.Whatcanbeinferredfromparagraph2aboutthedevelopmentofatollsaccordingtoDarwin’stheory?

¡Allatollsbeginasfringingreefs.

¡Anatollwillnotdevelopifanislandsubsidestooslowly.

¡Mostatollswilleventuallybecomebarrierreefs.

¡Theformationofalagoonacceleratestheoveralldevelopmentofanatoll.

Paragraph3

Sincethecurrentsurfacefeaturesofatollsgivenoevidenceofavolcanicbase,intheyearsafterthedevelopmentofDarwin’stheoryotherexplanationswereoffered,andthewholeconceptoftheoriginofatollsbecameembroiledinthecontroversyovertheoriginofcoralreefs.IfDarwin’stheorywascorrect,itmustbeassumedthatdrillingdownthroughthecurrentatollreefswouldyieldlayerafterlayerofreeflimestoneuntil,finally,volcanicrockwouldbeencountered.Theabilitytodrilltothebaseofatollreefsandresolvedtheproblemhadtowaituntilthemid-twentiethcenturyin1953.LaddandothergeologistsreportedboringsatEriwetokatollintheMarshallIslandsthatpenetrated1,283metersofreeflimestoneandthenhitvolcanicrock.ThiswastheevidencethatDarwin’stheorywassubstantiallycorrect.Thecorrectnessofthistheoryhasbeenstrengthenedbythediscoveryofflat-toppedmountainsorguyotsthat,atpresent,havetheirtopsmanyhundredsorthousandsofmetersbelowtheoceansurface,buthaveontheirsurfacetheremainsofshallowwatercorals.Evidently,thesemountainssanktoofastforreefgrowthtokeepabovetheoceansurface.

8.Theword“substantially”inthepassageisclosetinmeaningto

¡often

¡largely

¡probably

¡undoubtedly

9.Whichofthefollowingismentionedinparagraph3asthereasonmanyscientistsdoubtedDarwin’stheoryofhowatollsform?

¡AfterDarwin’sfive-yearvoyage,differentkindsofatollsthanthoseheobservedwerediscovered.

¡Sc