托福TPO2Part2閱讀原文及參考答案
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托福TPO2Part2閱讀原文
The Origins Of Cetaceans
It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals. They breathe through lungs, not through gills, and give birth to live young. Their streamlined bodies, the absence of hind legs, and the presence of a fluke1 and blowhole2 cannot disguise their affinities with land dwelling mammals. However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. 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. The fossil was officially named Pakicetus in honor of the country where the discovery was made. Pakicetus was found embedded in rocks formed from river deposits that were 52 million years old. The river that formed these deposits was actually not far from an ancient ocean known as the Tethys Sea.
The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossil provides precious details on the origins of cetaceans. The skull is cetacean-like but its jawbones lack the enlarged space that is filled with fat or oil and used for receiving underwater sound in modern whales. Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, 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 bred and gave birth on land.
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.
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
Fluke: the two parts that constitute the large triangular tail of a whale
1. "Blowhole: a hole in the top of the head used for breathing
Paragraph 1: It should be obvious that cetaceans-whales, porpoises, and dolphins-are mammals. They breathe through lungs, not through gills, and give birth to live young. Their streamlined bodies, the absence of hind legs, and the presence of a fluke3 and blowhole4 cannot disguise their affinities with land-dwelling mammals. However, unlike the cases of sea otters and pinnipeds (seals, sea lions, and walruses, whose limbs are functional both on land and at sea), it is not easy to envision what the first whales looked like. 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.
托福TPO2Part2閱讀題目
Directions: Mark your answer by filling in the oval next to your choice.
1. In paragraph 1, what does the author say about the presence of a blowhole in cetaceans?
It clearly indicates that cetaceans are mammals.
It cannot conceal the fact that cetaceans are mammals.
It is the main difference between cetaceans and land-dwelling mammals.
It cannot yield clues about the origins of cetaceans.
2. Which of the following can be inferred from paragraph 1 about early sea otters?
It is not difficult to imagine what they looked like
There were great numbers of them.
They lived in the sea only.
They did not leave many fossil remains.
Paragraph 3: The fossil consists of a complete skull of an archaeocyte, an extinct group of ancestors of modern cetaceans. Although limited to a skull, the Pakicetus fossil provides precious details on the origins of cetaceans. The skull is cetacean-like but its jawbones lack the enlarged space that is filled with fat or oil and used for receiving underwater sound in modern whales. Pakicetus probably detected sound through the ear opening as in land mammals. The skull also lacks a blowhole, another cetacean adaptation for diving. Other features, however, show experts that Pakicetus is a transitional form between a group of extinct flesh-eating mammals, the mesonychids, 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 bred and gave birth on land.
3. The word precious in the passage is closest in meaning to
Exact
Scarce
Valuable
Initial
4. Pakicetus and modern cetaceans have similar
Hearing structures
Adaptations for diving
Skull shapes
Breeding locations
5. The word it in the passage refers to
Pakicetus
Fish
Life
ocean
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.
●
●
●
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
托福TPO2Part2閱讀答案
參考答案：
1、2
2、1
3、3
4、3
5、1
6、2
7、4
8、4
9、2
10. 3
11. 4
12. 2
13-14. 1 2 5
托福TPO2Part2閱讀原文翻譯
沙漠已經(jīng)占據(jù)了地球表面積約四分之一，而且最近幾十年正以驚人的速度擴(kuò)張。沙漠化是指類似沙漠的環(huán)境漫延到原本并非沙漠的區(qū)域。據(jù)估計，地球表面另外四分之一的地方正面臨沙漠化威脅。
沙漠化主要通過以下過程實(shí)現(xiàn)：首先自然植被不斷減少，隨后風(fēng)力和雨水加速了土壤的腐蝕。有的時候松散的土壤全部被風(fēng)刮走，留下石質(zhì)化的表層;其它情況下細(xì)小的沙?？赡軙淮底?，而正常沙粒大小的砂子不斷堆積，從而形成移動的沙丘或者沙脊。
即便是在保留了土壤表層的區(qū)域，植被減少也已成為土壤大量吸取地下水的能力下降的典型因素。雨水對松散土壤的沖擊會把細(xì)小的粘土顆粒沖到土壤空隙中，封閉了土壤并降低土地表層水的滲透率。地表對水的吸收急劇減少，大量水資源流失，因此土壤的腐蝕率也隨即增加。地表吸收水分的能力進(jìn)一步弱化使得土壤越發(fā)干燥，導(dǎo)致植被的進(jìn)一步流失，于是便形成了土壤沙漠化的惡性循環(huán)。
在一些地方，沙漠面積的擴(kuò)大很大程度上歸因于干燥的氣候條件。在過去的幾千年里，不斷增加的溫室效應(yīng)使得一些地方干旱問題愈發(fā)嚴(yán)重。倘若空氣污染帶來的溫室效應(yīng)繼續(xù)惡化，沙漠化進(jìn)程會在未來數(shù)十年內(nèi)加速實(shí)現(xiàn)。
然而，可以肯定的是，大部分地區(qū)沙漠化主要都是由于人類活動造成，而非自然條件導(dǎo)致。沙漠邊緣的半干旱土地所處的生態(tài)平衡環(huán)境非常脆弱，環(huán)境壓力持續(xù)增加，而這些半干旱區(qū)域適應(yīng)環(huán)境壓力的能力極其有限。人口數(shù)量的增加使得人們不斷向土地施壓，依其提供食物和燃料。在濕潤的季節(jié)里，土地興許能夠應(yīng)付這些壓力。但是在干旱的季節(jié)里，在沙漠周邊的土地上，存在著這樣一個十分普遍的現(xiàn)象：人類對土地施加的壓力遠(yuǎn)遠(yuǎn)超過了土地自身減壓的能力，因此最終形成了沙漠。
導(dǎo)致沙漠化的主要因素有四個：過度種植，過度放牧，過分砍伐，過度灌溉。由于人口密度增加，人們對糧食作物的種植已經(jīng)擴(kuò)展到日益干燥的區(qū)域進(jìn)行。這些區(qū)域很有可能經(jīng)常會發(fā)生干旱，所以農(nóng)作物種植失敗是很正常的事情。大多數(shù)農(nóng)作物的種植需要事先移除天然植被，而農(nóng)作物欠收后又會留下大面積荒地，非常容易被風(fēng)力和雨水侵蝕。
在半干旱地區(qū)，草坪是主要的天然植被，家畜飼養(yǎng)是當(dāng)?shù)氐囊豁?xiàng)主要經(jīng)濟(jì)活動。在一個地區(qū)過量飼養(yǎng)家畜會導(dǎo)致植被覆蓋面積減少，土地被大量踐踏和碾碎。通常，隨之而來的就是土地硬化和加速侵蝕。
在很多國家木材是用來做飯和加熱的最主要燃料。人口增加帶來的壓力促使人們大量砍伐木材，導(dǎo)致許多城市和鄉(xiāng)村周圍大面積樹木和灌木減少。同時人們大量使用烘干的動物排泄物作為替代燃料同樣對土壤不利，因?yàn)檫@些珍貴的土壤成分調(diào)節(jié)劑和植物營養(yǎng)資源將不會再回歸至土壤當(dāng)中。
造成土地沙漠化的最后一個主要人為因素在于人類過度灌溉導(dǎo)致土壤的鹽堿化。灌溉多余的水滲透到地下水位。假如沒有排水系統(tǒng)的存在，那么地下水位上升，把溶解的鹽分帶到土壤表面。水分蒸發(fā)后，鹽分留在了表面，形成白色的地殼層，這一地殼層阻止了空氣和水接觸地底下的土壤。
沙漠化問題異常嚴(yán)重，這是因?yàn)橛衼鋸V闊的地區(qū)和數(shù)量龐大的人群都受到了沙漠化的影響，而且要想逆轉(zhuǎn)沙漠化的進(jìn)程甚至減緩沙漠化的速度都面臨著巨大的困難。一旦土壤被侵蝕，需要再經(jīng)過幾百到上千年的時間才會產(chǎn)生新的土壤。那些大量土壤仍保存完好的地方，亟需一個嚴(yán)謹(jǐn)而有力的保護(hù)政策和植被覆蓋計劃來保護(hù)現(xiàn)有土地。
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托福TPO2Part2閱讀原文及參考答案
