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1、TOEFLReading6Paragraph1:Itshouldbeobviousthatcetaceans-whales,porpoises,anddolphins-aremammals.Theybreathethroughlungs,notthroughgills,andgivebirthtoliveyoung.Theirstreamlinedbodies,theabsenceofhindlegs,andthepresenceofafluke3andblowhole4cannotdisguisetheiraffinitieswithland-dwelli
2、ngmammals.However,unlikethecasesofseaottersandpinnipeds(seals,sealions,andwalruses,whoselimbsarefunctionalbothonlandandatsea),itisnoteasytoenvisionwhatthefirstwhaleslookedlike.Extinctbut,alreadyfullymarinecetaceansareknownfromthefossilrecord.Howwasthegapbetweenawalkingmammalandaswi
3、mmingwhalebridged?Missinguntilrecentlywerefossilsclearlyintermediate,ortransitional,betweenlandmammalsandcetaceans.Fluke:thetwopartsthatconstitutethelargetriangulartailofawhale"Blowhole:aholeinthetopoftheheadusedforbreathing1.Inparagraph1,whatdoestheauthorsayaboutthepresenceofablow
4、holeincetaceans?○Itclearlyindicatesthatcetaceansaremammals.○Itcannotconcealthefactthatcetaceansaremammals.○Itisthemaindifferencebetweencetaceansandland-dwellingmammals.○Itcannotyieldcluesabouttheoriginsofcetaceans.Paragraph3:Thefossilconsistsofacompleteskullofanarchaeocyte,anextinc
5、tgroupofancestorsofmoderncetaceans.Althoughlimitedtoaskull,thePakicetusfossilprovidespreciousdetailsontheoriginsofcetaceans.Theskulliscetacean-likebutitsjawboneslacktheenlargedspacethatisfilledwithfatoroilandusedforreceivingunderwatersoundinmodernwhales.Pakicetusprobablydetectedsou
6、ndthroughtheearopeningasinlandmammals.Theskullalsolacksablowhole,anothercetaceanadaptationfordiving.Otherfeatures,however,showexpertsthatPakicetusisatransitionalformbetweenagroupofextinctflesh-eatingmammals,themesonychids,andcetaceans.IthasbeensuggestedthatPakicetusfedonfishinshall
7、owwaterandwasnotyetadaptedforlifeintheopenocean.Itprobablybredandgavebirthonland.3.Thewordpreciousinthepassageisclosestinmeaningto○Exact○Scarce○Valuable○Initial4.Pakicetusandmoderncetaceanshavesimilar(C)○Hearingstructures○Adaptationsfordiving○Skullshapes○Breedinglocations5.Thewordi
8、tinthepassagerefersto(A)○P
