托福阅读：TPO2(The Origins Of Cetaceans)原文及答案

　　Paragraph 4: Another major discovery was made in Egypt in 1989. Several skeletons of another early whale, Basilosaurus, were found in sediments left by the Tethys Sea and now exposed in the Sahara desert. This whale lived around 40 million years ago, 12 million years after Pakicetus. Many incomplete skeletons were found but they included, for the first time in an archaeocyte, a complete hind leg that features a foot with three tiny toes. Such legs would have been far too small to have supported the 50-foot-long Basilosaurus on land. Basilosaurus was undoubtedly a fully marine whale with possibly nonfunctional, or vestigial, hind legs.

　　6. The word exposed in the passage is closest in meaning to

　　Explained

　　Visible

　　Identified

　　Located

　　7. The hind leg of Basilosaurus was a significant find because it showed that Basilosaurus

　　Lived later than Ambulocetus natans

　　Lived at the same time as Pakicetus

　　Was able to swim well

　　Could not have walked on land

　　8. It can be inferred that Basilosaurus bred and gave birth in which of the following locations

　　On land

　　Both on land and at sea

　　In shallow water

　　In a marine environment

　　Paragraph 5: An even more exciting find was reported in 1994, also from Pakistan. The now extinct whale Ambulocetus natans ("the walking whale that swam") lived in the Tethys Sea 49 million years ago. It lived around 3 million years after Pakicetus but 9 million before Basilosaurus. The fossil luckily includes a good portion of the hind legs. The legs were strong and ended in long feet very much like those of a modern pinniped. The legs were certainly functional both on land and at sea. The whale retained a tail and lacked a fluke, the major means of locomotion in modern cetaceans. The structure of the backbone shows, however, that Ambulocetus swam like modern whales by moving the rear portion of its body up and down, even though a fluke was missing. The large hind legs were used for propulsion in water. On land, where it probably bred and gave birth, Ambulocetus may have moved around very much like a modern sea lion. It was undoubtedly a whale that linked life on land with life at sea

　　9. Why does the author use the word luckily in mentioning that the Ambulocetus natans fossil included hind legs?

　　Fossil legs of early whales are a rare find.

　　The legs provided important information about the evolution of cetaceans.

　　The discovery allowed scientists to reconstruct a complete skeleton of the whale.

　　Until that time, only the front legs of early whales had been discovered.

　　10. Which of the sentences below best expresses the essential information in the highlighted sentence in the passage?

　　Incorrect choices change the meaning in important ways or leave out essential information.

　　Even though Ambulocetus swam by moving its body up and down, it did not have a backbone.

　　The backbone of Ambulocetus, which allowed it to swim, provides evidence of its missing fluke.

　　Although Ambulocetus had no fluke, its backbone structure shows that it swam like modern whales.

　　By moving the rear parts of their bodies up and down, modern whales swim in a different way from the way Ambulocetus swam.

　　11. The word propulsion in the passage is closest in meaning to

　　Staying afloat

　　Changing direction

　　Decreasing weight

　　Moving forward

　　Paragraph 1: Extinct but already fully marine cetaceans are known from the fossil record. ■How was the gap between a walking mammal and a swimming whale bridged? ■Missing until recently were fossils clearly intermediate, or transitional, between land mammals and cetaceans.■Very exciting discoveries have finally allowed scientists to reconstruct the most likely origins of cetaceans. ■In 1979, a team looking for fossils in northern Pakistan found what proved to be the oldest fossil whale.

　　12. Look at the four squares [■] that indicate where the following sentence can be added to the passage.

　　This is a question that has puzzled scientists for ages.

　　Where would the sentence best fit?

　　13-14. 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 choices do not belong in the summary because they express ideas that are not presented in the passage or are minor ideas in the passage. This question is worth 2 points.

　　This passage discusses fossils that help to explain the likely origins of cetaceans-whales, porpoises, and dolphins.

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　　Answer Choices

　　1. Recent discoveries of fossils have helped to show the link between land mammals and cetaceans.

　　2. The discovery of Ambulocetus natans provided evidence for a whale that lived both on land and at sea.

　　3. The skeleton of Basilosaurus was found in what had been the Tethys Sea, an area rich in fossil evidence.

　　4. Pakicetus is the oldest fossil whale yet to be found.

　　5. Fossils thought to be transitional forms between walking mammals and swimming whales were found.

　　6. Ambulocetus' hind legs were used for propulsion in the water.