托福閱讀tpo-2-The-Origins-of-Cetaceans鯨類的起源原題解析.

1、閱讀原文：?Itshould be obviousthatcetaceans-whales,porpoises,and dolphins-aremammals.They breathe through lungs, not through gills, and give birth to live young. Theirstreamlined bodies, the absence of hind legs, and the presence of a fluke1 andblowhole2 cannot disguisetheiraffinities withland dwellingma

2、mmals.However,unlike the casesof sea otters and pinnipeds(seals,sea lions, andwalruses, whoselimbs are functional both on land and at sea), it is not easy to envision what thefirst whaleslooked like.Extinctbut already fullymarinecetaceans are known fromthe fossil record. How was the gap between a wa

3、lking mammal and a swimming whalebridged? Missinguntil recently were fossilsclearlyintermediate,or transitional,between land mammals and cetaceans.眾所周知，鯨類動物是哺乳動物, 如鯨魚、鼠海豚和海豚。它們用肺呼吸，而不是鰓，屬于胎生。 鯨類動物呈流線型的身體，后腿的消失， 尾片和氣孔的出現(xiàn)，這些 特征都不能掩飾它們和陸生哺乳動物的相似之處。然而，想知道世上第一只鯨長什么樣并非易事，不像還原海獺及鰭足類動物（四肢水陸兩用如海豹，海獅，海象）的原貌那么

4、簡單。一些完全水生的鯨類動物雖然已經(jīng)滅絕，但仍可通過化石來對它們進行考察。陸棲哺乳動物和海洋鯨類之間有何聯(lián)系？近期發(fā)現(xiàn)的化石已經(jīng)可以很清晰地幫助人們了解這個問題，以及他們之間的過渡關(guān)系。Very excitingdiscoverieshave finallyallowed scientiststoreconstructthe mostlikelyoriginsof cetaceans.In 1979, a team lookingfor fossils innorthernPakistanfound what proved to be the oldest fossil whale. The

5、fossil was officially namedPakicetus inhonor of the country where thediscovery was made. Pakicetus was foundembedded in rocksformed fromriverdepositsthatwere 52 millionyears old.The riverthat formed these deposits was actually not far from an ancient ocean known as theTethys Sea.科學家們通過一些令人振奮的發(fā)現(xiàn)重現(xiàn)了鯨類

6、動物幾近真實的起源。1979 年，在巴基斯坦北部，一個尋找化石的考察隊發(fā)掘到了最古老的鯨魚化石。這塊化石被官方命名為Pakicetus ，以紀念人們發(fā)現(xiàn)它的地方。這塊化石是在一條河的沉積巖中發(fā)現(xiàn)的，這條河有5200 萬年的歷史，離古地中海不遠.The fossil consists of a complete skull of an archaeocyte, an extinct group ofancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossilprovides precious de

7、tails on the origins of cetaceans. The skull is cetacean-likebutitsjawboneslack the enlargedspace thatis filledwith fatoroiland used forreceiving underwater sound in modern whales. Pakicetus probably detected soundthroughthe earopeningas inlandmammals. The skullalso lacksa blowhole,anothercetaceanad

8、aptation fordiving.Otherfeatures,however, show expertsthatPakicetusisa transitionalformbetweenagroup ofextinctflesh-eatingmammals, themesonychids, and cetaceans. It has been suggested that Pakicetus fed on fish in shallow water and was not yet adapted for life in the open ocean. It probably bredand

9、gave birth on land.Pakicetus包括一個完整原始動物的頭蓋骨，它的主人是現(xiàn)代鯨類的祖先。盡管只是個頭蓋骨，但它卻提供了研究原始鯨類動物起源的珍貴信息。這個頭蓋骨和鯨類動物的很像，但它的下頜骨和現(xiàn)代鯨類略有不同，現(xiàn)代鯨類動物的下頜骨中含有額外的空間儲存脂肪或者油脂來吸收水下的聲音。 Pakicetus的主 人可能會像陸生哺乳動物那樣通過張開的耳朵來探測聲音。另外，這個頭蓋骨沒有呼吸孔，而鯨類動物有，這便是鯨類動物為了適應(yīng)水生環(huán)境的另一種適應(yīng)性表現(xiàn)。然而，專家認為 Pakicetus的其它特征表明它們是已滅絕的食肉哺乳動物（中獸科動物） 和鯨類動物的過渡型。有人認為 Pak

10、icetus靠吃淺水的魚類為生， 未能適應(yīng)在遼闊的大海里生活。它們很有可能在陸地進行生育繁殖。Anothermajor discovery was made in Egyptin1989. Severalskeletonsof anotherearly whale, Basilosaurus, were found in sediments left by the Tethys Sea and nowexposed inthe Sahara desert. This whale livedaround40 millionyears ago,12 millionyears after Pakic

11、etus. Many incomplete skeletons were found but they included, forthefirsttime in an archaeocyte,a completehindlegthatfeaturesa footwith threetinytoes.Such legswouldhave been far toosmalltohave supportedthe 50-foot-longBasilosauruson land.Basilosauruswas undoubtedlya fullymarine whale with possiblyno

12、nfunctional, or vestigial, hind legs.1989 年，在埃及有了另一個重大發(fā)現(xiàn)。人們在古地中海殘留的沉積物中發(fā)現(xiàn)了另一類早期鯨魚 Basilosaurus的一些骨骸， 這些骨骸如今暴露在撒哈拉大沙漠上。 Basilosaurus生活在大約4000 萬年前，比Pakicetus 鯨魚晚了 1200 萬年。盡管發(fā)現(xiàn)的這些骨骼并不完整，但這是專家們第一次在原始動物身上發(fā)現(xiàn)完整的后肢，它有三個小腳趾作為的足部特征?？蛇@些后肢還太小， 遠無法支撐50 英尺長的 Basilosaurus在陸地行走。 因 此，Basilosaurus必定是完全水生的鯨魚，它們的后肢已經(jīng)不起

13、任何作用，或者說已經(jīng)退化.An even more exciting find was reported in 1994, also from Pakistan. The nowextinctwhaleAmbulocetusnatans("thewalkingwhale thatswam") livedinthe TethysSea 49 millionyearsago. Itlivedaround 3 millionyears after Pakicetusbut 9 millionbefore Basilosaurus. The fossil luckily inclu

14、des a good portion of the hind legs.The legswere strongand ended inlongfeet verymuch likethoseofa modern pinniped.The legswere certainlyfunctionalboth on landand at sea. The whale retained a tailand lackeda fluke, themajor means oflocomotioninmodern cetaceans.The structureof the backbone shows, howe

15、ver, that Ambulocetus swam like modern whales by movingtherearportion ofitsbody up and down, even though a flukewas missing.The largehindlegs were used forpropulsionin water.On land,where itprobablybred and gavebirth, Ambulocetus may have moved around very much like a modern sea lion. It was undoubt

16、edly a whale that linked life on land with life at sea.1. Fluke: the two parts that constitute the large triangular tail of a whale2. Blowhole: a hole in the top of the head used for breathing1994 年，巴基斯坦報道了一個更令人興奮的發(fā)現(xiàn)。目前已經(jīng)滅絕的鯨魚Ambulocetusnatans（可以步行的鯨類）4900 萬年前曾在古地中海生活過。 比 Pakicetus晚大約 300 萬年，比 Basil

17、osaurus 早 900萬年左右。幸運的是，被發(fā)現(xiàn)的Ambulocetus natans 保留著完整的后肢。它的后肢很強壯，底部有長足，非常像現(xiàn)在的鰭足類動物。這些后肢使得他們既能在陸地行走又能在海里游行。雖然Ambulocetus natans保留了尾巴，但它們?nèi)鄙佻F(xiàn)代水生鯨類動物用于行動的主要身體部位尾片。不過，從Ambulocetus 的脊椎結(jié)構(gòu)上可以看出，即使缺少尾 片，它們也能像現(xiàn)代鯨魚那樣通過身體背部的上下擺動來游走。大的后肢通常被當作是水中前行的發(fā)動機。在它們可能交配繁殖的陸地上，Ambulocetus行動起來非常像現(xiàn)代海獅。毫無疑問，鯨魚是連接著陸地生命和海洋生命的物種。第

18、1題：In paragraph 1, what does the author say about the presence of a blowhole in cetaceans?A： It clearly indicates that cetaceans are mammals.B： It cannot conceal the fact that cetaceans are mammals.C： It is the main difference between cetaceans and land-dwelling mammals.D： It cannot yield clues abou

19、t the origins of cetaceans.解析：根據(jù)blowhole查找原文，找到：the presence of a fluke1 and blowhole2 cannotdisguise their affinities with land dwelling mammals.選項 B 正確，是對該句的同義改寫。A 錯誤，反了。C 錯誤，沒有提到。D 錯誤，沒有提到。第 2題：Which ofthe following can be inferred fromparagraph 1 about earlysea otters?A： It is not difficult to i

20、magine what they looked likeB： There were great numbers of them.C： They lived in the sea only.D： They did not leave many fossil remains解析：典型取非推理題。根據(jù) sea otters 定位原文，找到： unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both onland and at sea), i

21、t is not easy to envision what the first whales looked like。A正確。BCD都不能推出。第 3題：The word precious in the passage is closest in meaning toA： ExactB： ScarceC： ValuableD： Initial解析：This is a Vocabulary question. The word being tested is precious. It is highlighted in the passage. The correctanswer is cho

22、ice 3, "valuable." Anything that is precious is very important and therefore valuable.第 4題：Pakicetus and modern cetaceans have similarA： Hearing structuresB： Adaptations for divingC： Skull shapesD： Breeding locations解析：根據(jù) P 定位 2 段、 3 段， 3 段提到： The skull is cetacean-like，所以 C正確。A 反。B 沒有提到。D

23、 反。第 5題：The word it in the passage refers toA： PakicetusB： FishC： LifeD： ocean解析：指代題，根據(jù)前句，It has been suggested that Pakicetus fed on fish in shallowwater and was not yet adapted for life in the open ocean。說的就是P，所以選A第 6題：The word exposed in the passage is closest in meaning toA： ExplainedB： VisibleC

24、： IdentifiedD： Located解析：This is a Vocabulary question. The word being tested is exposed. It is highlighted in the passage. The correctanswer is choice 2, "visible." Exposed means "uncovered." A skeleton that is uncovered can be seen. Visiblemeans "can be seen."第 7題：The

25、 hind leg of Basilosaurus was a significant find because it showed that BasilosaurusA： Lived later than Ambulocetus natansB： Lived at the same time as PakicetusC： Was able to swim wellD： Could not have walked on land解析：根據(jù) Basilosaurus定位在 4 段，or the firsttime in an archaeocyte,a complete hindleg that

26、featuresa footwiththreetinytoes.Such legswould have been fartoo smallto have supported the 50-foot-long Basilosaurus on land. D選項是同義改寫，正確。ABC明顯錯誤。第 8題：It can be inferred that Basilosaurus bred and gave birth in which of the following locationsA： On landB： Both on land and at seaC： In shallow waterD：

27、 In a marine environment解析：推理題。 依據(jù)此句： Basilosauruswas undoubtedlya fullymarine whale with possiblynonfunctional, or vestigial, hind legs.B是完全海洋動物，可知選項D 正確。ABC明顯不能推出。倒數(shù)第二段第 9題：Why does the author use the word luckily in mentioning that the Ambulocetus natans fossil included hind legs?A： Fossil legs o

28、f early whales are a rare find.B： The legs provided important information about the evolution of cetaceans.C： The discovery allowed scientists to reconstruct a complete skeleton of the whale.D： Until that time, only the front legs of early whales had been discovered.解析：正確選項肯定在A和 B 之間。哪個更好呢？由后句內(nèi)容：The

29、 legswere strongand endedin long feet very much like those of a modern pinniped. The legs were certainlyfunctional both on land and at sea. The whale retained a tail and lacked a fluke,the major means of locomotion in modern cetaceans.可知 hind leg提供了很多有價值信息。所以B 正確。 A 并不能從這些話中推出。第 10題：Which of the sen

30、tences below best expresses the essential information in thehighlighted sentence in the passage?Incorrect choices change the meaning in important ways or leave out essential information.A： Even though Ambulocetus swam by moving its body up and down, it did not have a backbone.B： The backbone of Ambu

31、locetus, which allowed it to swim, provides evidence of its missing fluke.C： Although Ambulocetus had no fluke, its backbone structure shows that it swam like modern whales.D： By moving the rear parts of their bodies up and down, modern whales swim in a different way from the way Ambulocetus swam.解析

32、：Thisisa Sentence Simplificationquestion.As withallof theseitems,a singlesentence in the passage ishighlighted:The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving therear portion of its body up and down, even though a fluke was missing.Choice 3 is the bes

33、t answer because it contains all of the essential information in the highlighted sentence.Choice 1 is not true because Ambulocetus did have a backbone. Choice 2 is not true because the sentencesays that the backbone showed how the Ambulocetus swam, not that itwas missinga fluke. Choice 4 isuntrue be

34、cause the sentence states that Ambulocetus and modern whales swam in the same way.第 11題：The word propulsion in the passage is closest in meaning toA： Staying afloatB： Changing directionC： Decreasing weightD： Moving forward解析：This isa Vocabulary question. The wordbeingtested ispropulsion.It ishighlig

35、hted in the passage. Choice 4,"moving forward" is the best answer because it means the action of propelling.The whale in the sentenceused its hind legs to push itself forward in the water.第 12題：Look at the four squares that indicate where the following sentence can be added to the passage.

36、 Where would the sentence best fit?This is a question that has puzzled scientists for ages.解析：插入句中 This is a questionthathas puzzled前句最好是個疑問。明顯是B 位置最合適scientistsforages. 含有一個 question,第 13題：Directions: An introductory sentence for a brief summary of the passage is provided below. Complete the summary by selecting the THREE answer choices that express the most important ideas in the passage. Some answer choic