【单选题】C、
Ifadiversurfacestooquickly,hemaysufferthebends.Nitr ogen(氮)dissolved(溶解)inhisbloodissuddenlyliberatedbythereductionofpressure.Theconsequence,ifthebubbles(气泡)accumulateinajoint,issharppainandabentbody—thusthename.Ifthebubblesforminhislungsorhisbrain,theconsequencecanbedeath.Otherair-breathinganimalsalsosufferthisdecompression(减压)sicknessiftheysurfacetoofast:whales,forexample.Andso,longago,didichthyosaurs.Thattheseancientseaanimalsgotthebendscanbeseenfromtheirbones.Ifbubblesofnitr ogenforminsidethebonetheycancutoffitsbloodsupply.Thiskillsthecellsinthebone,andconsequentlyweakensit,sometimestothepointofcollapse.Fossil(化石)bonesthathavecavedinonthemselvesarethusasignthattheanimaloncehadthebends.BruceRothschildoftheUniversityofKansasknewallthiswhenhebeganastudyofichthyosaurbonestofindouthowwidespreadtheproblemwasinthepast.Whatheparticularlywantedtoinvestigatewashowichthyosaursadaptedtotheproblemofdecompressionoverthe150millionyears.Tothisend,heandhiscolleaguestr aveledtheworld’snatural-historymuseums,lookingathundredsofichthyosaursfromtheTriassicperiodandfromthelaterJurassicandCretaceousperiods. Whenhestarted,heassumedthatsignsofthebendswouldberarerinyoungerfossils,reflectingtheirgradualevolutionofmeasurestodealwithdecompression.Instead,hewasastonishedtodiscovertheopposite.Morethan15%ofJurassicandCretaceousichthyosaurshadsufferedthebendsbeforetheydied,butnotasingleTriassicspecimen(标本)showedevidenceofthatsortofinjury.Ifichthyosaursdidevolveananti-decompressionmeans,theyclearlydidsoquickly—and,moststr angely,theylostitafterwards.ButthatisnotwhatDrRothschildthinkshappeneD、Hesuspectsitwasevolutioninotheranimalsthatcausedthechange.Whalesthatsufferthebendsoftendosobecausetheyhavesurfacedtoescapeapredator(捕食动物)suchasalargeshark.OneofthefeaturesofJurassicoceanswasanabundanceoflargesharksandcrocodiles,bothofwhichwerefondofichthyosaurlunches.Triassicoceans,bycontr ast,weremercifullyshark-andcrocodile-free.IntheTriassic,then,ichthyosaursweretopofthefoodchain.IntheJurassicandCretaceous,theywereprey(猎物)aswellaspredator—andoftenhadtomakeaspeedyexitasaresult.ThepurposeofRothschild’sstudyistosee________.A．howoftenichthyosaurscaughtthebendsB、howichthyosaursadaptedtodecompressionC．whyichthyosaursbenttheirbodiesD．whenichthyosaursbroketheirbones
