托福閱讀真題分類推論題(二)

眾所周知，托福閱讀素來是中國考生的單薄項(xiàng)，我們?yōu)閹椭鷱V大托?？忌蚱崎喿x瓶頸，提升托福閱讀成績，特意精心整理了托福閱讀真題分類素材庫。那快來看看托福閱讀推論題集錦吧！TheOriginsofCetaceansItshouldbeobviousthatcetaceans—whales,porpoises,anddolphins—aremammals.Theybreathethroughlungs,notthroughgills,andgivebirthtoliveyoung.Theirstreamlinedbodies,theabsenceofhindlegs,andthepresenceofafluke1andblowhole2cannotdisguisetheiraffinitieswithlanddwellingmammals.However,unlikethecasesofseaottersandpinnipeds(seals,sealions,andwalruses,whoselimbsarefunctionalbothonlandandatsea),itisnoteasytoenvisionwhatthefirstwhaleslookedlike.Extinctbutalreadyfullymarinecetaceansareknownfromthefossilrecord.Howwasthegapbetweenawalkingmammalandaswimmingwhalebridged?Missinguntilrecentlywerefossilsclearlyintermediate,ortransitional,betweenlandmammalsandcetaceans.Veryexcitingdiscoverieshavefinallyallowedscientiststoreconstructthemostlikelyoriginsofcetaceans.In1979,ateamlookingforfossilsinnorthernPakistanfoundwhatprovedtobetheoldestfossilwhale.ThefossilwasofficiallynamedPakicetusinhonorofthecountrywherethediscoverywasmade.Pakicetuswasfoundembeddedinrocksformedfromriverdepositsthatwere52millionyearsold.TheriverthatformedthesedepositswasactuallynotfarfromanancientoceanknownastheTethysSea.Thefossilconsistsofacompleteskullofanarchaeocyte,anextinctgroupof1/5ancestorsofmoderncetaceans.Althoughlimitedtoaskull,thePakicetusfossilprovidespreciousdetailsontheoriginsofcetaceans.Theskulliscetacean-likebutitsjawboneslacktheenlargedspacethatisfilledwithfatoroilandusedforreceivingunderwatersoundinmodernwhales.Pakicetusprobablydetectedsoundthroughtheearopeningasinlandmammals.Theskullalsolacksablowhole,anothercetaceanadaptationfordiving.Otherfeatures,however,showexpertsthatPakicetusisatransitionalformbetweenagroupofextinctflesh-eatingmammals,themesonychids,andcetaceans.IthasbeensuggestedthatPakicetusfedonfishinshallowwaterandwasnotyetadaptedforlifeintheopenocean.Itprobablybredandgavebirthonland.AnothermajordiscoverywasmadeinEgyptin1989.Severalskeletonsofanotherearlywhale,Basilosaurus,werefoundinsedimentsleftbytheTethysSeaandnowexposedintheSaharadesert.Thiswhalelivedaround40millionyearsago,12millionyearsafterPakicetus.Manyincompleteskeletonswerefoundbuttheyincluded,forthefirsttimeinanarchaeocyte,acompletehindlegthatfeaturesafootwiththreetinytoes.Suchlegswouldhavebeenfartoosmalltohavesupportedthe50-foot-longBasilosaurusonland.Basilosauruswasundoubtedlyafullymarinewhalewithpossiblynonfunctional,orvestigial,hindlegs.Anevenmoreexcitingfindwasreportedin1994,alsofromPakistan.ThenowextinctwhaleAmbulocetusnatans("thewalkingwhalethatswam")livedintheTethysSea49millionyearsago.Itlivedaround3millionyearsafterPakicetusbut9millionbeforeBasilosaurus.Thefossilluckilyincludesagoodportionofthehind2/5legs.Thelegswerestrongandendedinlongfeetverymuchlikethoseofamodernpinniped.Thelegswerecertainlyfunctionalbothonlandandatsea.Thewhaleretainedatailandlackedafluke,themajormeansoflocomotioninmoderncetaceans.Thestructureofthebackboneshows,however,thatAmbulocetusswamlikemodernwhalesbymovingtherearportionofitsbodyupanddown,eventhoughaflukewasmissing.Thelargehindlegswereusedforpropulsioninwater.Onland,whereitprobablybredandgavebirth,Ambulocetusmayhavemovedaroundverymuchlikeamodernsealion.Itwasundoubtedlyawhalethatlinkedlifeonlandwithlifeatsea.翻譯鯨類的起源很明顯，鯨類鯨魚、江豚和海豚都是哺乳動(dòng)物。它們經(jīng)過肺呼吸，而不是經(jīng)過鰓呼吸，并生育出年輕的生命。它們流線型的身體，沒有后腿，以及有一個(gè)波折平和孔，這些都不能夠掩蓋它們與陸地哺乳動(dòng)物的親緣關(guān)系?？墒?，與海獺和鰭足動(dòng)物（海豹、海獅和海象，它們的四肢在陸地和海上都有功能）不同樣，要想象第一批鯨魚長什么樣其實(shí)不簡(jiǎn)單。已經(jīng)滅絕但已經(jīng)完滿部是海洋鯨目動(dòng)物的化石記錄是已知的。一只會(huì)走路的哺乳動(dòng)物和一只會(huì)游泳的鯨魚之間的鴻溝是如何彌合的？直到近來才發(fā)現(xiàn)明顯介于陸生哺乳動(dòng)物和鯨目動(dòng)物之間的中間或過渡化石。特別令人愉悅的發(fā)現(xiàn)終于使科學(xué)家們能夠重建鯨目動(dòng)物最可能的起源。1979年，一個(gè)在巴基斯坦北部搜尋化石的小組發(fā)現(xiàn)了被證明是最古老的鯨魚化石。為了紀(jì)念這個(gè)發(fā)現(xiàn)的國家，這塊化石被正式命名為Pakicetus。帕克塞特斯被發(fā)現(xiàn)埋在5200萬年前河流聚積物形成的巖石中。形成這些聚積物的河流實(shí)質(zhì)上離被稱為特提斯海的遠(yuǎn)洋不遠(yuǎn)。3/5這個(gè)化石由一個(gè)原始細(xì)胞的完滿頭骨組成，原始細(xì)胞是現(xiàn)代鯨目動(dòng)物滅絕的祖先。誠然僅限于頭骨，但帕基塞特斯化石供應(yīng)了鯨目動(dòng)物起源的可貴細(xì)節(jié)。頭骨像鯨目動(dòng)物，但它的下顎骨缺少充滿脂肪或油的擴(kuò)大空間，用于接收現(xiàn)代鯨魚的水下聲音。Pakicetus可能經(jīng)過耳朵的張口探測(cè)到聲音，就像陸地哺乳動(dòng)物同樣。頭骨也沒有氣孔，這是另一種鯨類潛水的適應(yīng)。可是，其他的特色也向?qū)＜覀儽硎?，白鼬是一種介于滅絕的食肉哺乳動(dòng)物、中甲目動(dòng)物和鯨目動(dòng)物之間的過渡物種。有人認(rèn)為，白鰭豚在淺水中以魚為食，還不適合在公海生活。它可能在陸地上生殖和生育。另一個(gè)重要發(fā)現(xiàn)是1989年在埃及發(fā)現(xiàn)的。在特提斯海留下的聚積物中發(fā)現(xiàn)了另一種早期鯨魚的骨骼，即龍龍，現(xiàn)在裸露在撒哈拉沙漠中。這條鯨魚生活在大體4000萬年前，比帕克塞圖斯早1200萬年。發(fā)現(xiàn)了好多不完滿的骨骼，但它們首次在原始細(xì)胞中包括完滿的后腿，其特色是一只腳有三個(gè)小腳趾。這樣的腿太小了，支撐不住陸地上50英尺長的龍舌龍。毫無疑問，龍舌龍是一種完滿海洋性的鯨魚，后腿可能沒有功能，或是剩余。1994年報(bào)道了一個(gè)更令人愉悅的發(fā)現(xiàn)，同樣來自巴基斯坦。現(xiàn)在已經(jīng)滅絕的鯨豚（Ambulocetusnatans）生活在4900萬年前的特提斯海。它生活在帕克塞特斯此后約300萬年，但在基龍龍從前約900萬年。好運(yùn)的是，這塊化石的后腿有很大一部分。它們的腿很強(qiáng)壯，尾端是很長的腳，特別像現(xiàn)代的鰭足動(dòng)物。這兩條腿在陸地和海上都能正常工作。鯨魚保留了一條尾巴，缺少一個(gè)僥幸，這是現(xiàn)代鯨目動(dòng)物的主要運(yùn)動(dòng)方式?？墒?，脊骨的結(jié)構(gòu)顯示，盡管缺少了一只僥幸，但它的身體后部上下搬動(dòng)，就像現(xiàn)代鯨魚同樣游動(dòng)。大后腿被用來在水中推進(jìn)。在陸地上，它可能在那處繁衍生息，安布洛塞特斯可能像現(xiàn)代海獅同樣各處走動(dòng)。毫無疑問，它是一頭將陸地上的生命與海上的生命聯(lián)系在一起的鯨魚。Paragraph4:AnothermajordiscoverywasmadeinEgyptin1989.Severalskeletonsofanotherearlywhale,Basilosaurus,werefoundinsedimentsleftbythe4/5TethysSeaandnowexposedintheSaharadesert.Thiswhalelivedaround40millionyearsago,12millionyearsafterPakicetus.Manyincompleteskeletonswerefoundbuttheyincluded,forthefirsttimeinanarchaeocyte,acompletehindlegthatfeaturesafootwiththreetinytoes.Suchlegswouldhavebeenfartoosmalltohavesupportedthe50-foot-longBasilosaurusonland.Basilosauruswasundoubtedlyafullymarinewhalewithpossiblynonfunctional,or