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If a diver surfaces too quickly, he may suffer thebends. Nitrogen (氮) dissolved (溶 解) in his blood issuddenly liberated by the reduction of pressure.The consequence, if t he bubbles (气 泡) accumulatein a joint, is sharp pain and a bent body—thus thename. If the bubbles f orm in his lungs or his brain,the consequence can be death. Other air-breathing animals also suffer this decompression (减 压) sickness if they surface toofast: whales, for example. And so, long ago, did ichthyosau rs. That these ancient sea animalsgot the bends can be seen from their bones. If bubbles of nitrogen form inside the bone theycan cut off its blood supply. This kills the cells in the bone, and consequently weakens it,sometimes to the point of collapse. Fossil (化 石)bones that have caved in on themselves arethus a sign that the animal once had the be nds. Bruce Rothschild of the University of Kansas knew all this when he began a study of ichthy osaurbones to find out how widespread the problem was in the past. What he particularl y wantedto investigate was how ichthyosaurs adapted to the problem of decompression over the 150million years. To this end, he and his colleagues traveled the world's naturalhistory museums,looking at hundreds of ichthyosaurs from the Triassicperiod and from the later Jurassic andCretaceous periods. When he started, he assumed that signs of the bends would be rarer in younger fossils,re flecting their gradual evolution of measures to deal with decompression. Instead, he was astonished to discover the opposite. More than 15% of Jurassic and Cretaceous ichthyos aurshad suffered the bends before they died, but not a single Triassic specimen (标 本) showedevidence of that sort of injury. If ichthyosaurs did evolve an anti-decompression means, they clearly did so quickly—and, moststrangely, they lost it afterwards. But that is not what Dr Rothschild thinks happened . Hesuspects it was evolution in other animals that caused the change. Whales that suffer the bends often do so because they have surfaced to escape a predat or( 捕 食 动 物 ) such as a large shark. One of the features of Jurassic oceans was an abundance oflar ge sharks and crocodiles, both of which were fond of ichthyosaur lunches. Triassic oceans, bycontrast, were mercifully shark- and crocodile-free. In the Triassic, then, ichthyosaur s were topof the food chain. In the Jurassic and Cretaceous, they were prey ( 猎 物) as well as predator—and often had to make a speedy exit as a result. 61. Which of the following is a typical symptomof the bends? A. A twisted body. B. A gradual decrease in blood supply. C. A sudden release of nitrogen in blood. D. A drop in blood pressure. 62. The purpose of Rothschild's study is to see ______. A. how often ichthyosaurs caught the bends

B. how ichthyosaurs adapted to decompression C. why ichthyosaurs bent their bodies D. when ichthyosaurs broke their bones 63. Rothschild's finding stated in Paragraph 4 ______. A. confirmed his assumption B. speeded up his research process C. disagreed with his assumption D. changed his research objectives 64. Rothschild might have concluded that ichthyosaurs ______. A. failed to evolve an anti-decompression means B. gradually developed measures against the bends C. died out because of large sharks and crocodiles D. evolved an anti-decompression means but soon lost it

如果一个潜水员过快地浮出水面,那么他的身体有可能会弯曲。而溶解在他血液里氮会因压力减小而突然 释放。因此,如果氮气泡在他的关节里积累,会造成剧烈的疼痛,而弯曲的身体也是因此而得名。如果气 泡在他的肺部或他的大脑里形成,那么结果可能会导致死亡。 如果其他呼吸空气的动物过快地浮出水面,它们也会遭受这种因减压而带来的疾病,例如鲸鱼。还有很久 以前被称作是鱼龙的海洋动物也是如此。我们可以从它们的骨头看出这些古老的海洋动物的身体是弯曲 的。如果泡沫氮在骨内形成,那么它们就可以切断血液供给。这会杀死骨头里的细胞,最后会弱化骨头的 功能,有时甚至会导致骨头坏死。因此,在它们身上发掘出来的骨骼化石就是它们的身体曾经弯曲过的记 录。 当他开始研究鱼龙骨并发现了过去普遍存在的问题时, 堪萨斯大学的布鲁斯· 罗斯柴尔德明白了这一切。 他 特别想调查的是 1.5 亿年的鱼龙是如何适应减压问题的。为此,他和他的同事们环游了世界上的自然历史 博物馆,看了成百上千个鱼龙化石,其中有三迭纪时期的,有侏罗纪晚期的,还有白垩纪时期的。 当他开始研究时,他认为这种弯曲现象在年轻的化石中会比较罕见,这反映出他们处理减压问题的渐变过 程。但恰恰相反,他惊讶地得出相反的结果。超过 15%的侏罗纪和白垩纪时期的鱼龙在死前身体曾变弯 过,但却没有一个三迭纪时期的标本能找出受过这种伤的迹象。 如果鱼龙是以一种逆压力的方式进化的话,那么很显然,它们进化的速度太快了,而且,更令人奇怪的是 后来它们消失了。但罗斯柴尔德博士并不认为会发生的这种事。他怀疑这是其他动物进化所引发的变化。 身体弯曲的鲸经常这么做,因为他们必须浮出水面以躲避像大型鲨鱼这样的捕食者。侏罗纪时期的海洋特 色之一在于它有大量的大鲨鱼和鳄鱼,这两者都喜欢以鱼龙为食。相比之下,三迭纪时期的海洋中鲨鱼都 比较温和,也没有鳄鱼。因而在三迭纪时期,鱼龙处在食物链的顶端。在侏罗纪和白垩纪时期,它们既是 猎物也是捕食者,因此经常不得不快速逃离。 61. A 考查细节理解。由文章第一句及第一段中的 "Theconsequence...is sharp pain and a bent body"可知,减压病的典型症状是身体弯曲,因此 答案是 A。 62. B 考查细节理解。根据文章第三段第二句话可知,Rothschild 的研究目的是调查鱼龙如何适应减压, 因此 B 项正确。 63. C 考查细节理解。根据文章第四段中的 "Instead, he was astonished to discover the opposite."可知,Rothschild 研究的结果与他之前 的假设相反。 64. A 考查推理判断。文章最后一段提到在三纪时期鱼龙处在食物链的顶层,因此它们不必迅速地躲避捕 食者,这导致了它们没有形成反减压能力。

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