If a diver surfaces too quickly.he may suffer the bends．Nitrogen in his blood is suddenly liberated by the reduction of pressure．The consequence.if the bubbles accumulate in a joint.is sharp pain an 题目和参考答案——青夏教育精英家教网—

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13．If a diver surfaces too quickly，he may suffer the bends．Nitrogen（氮） dissolved（溶解） in his blood is suddenly liberated by the reduction of pressure．The consequence，if the bubbles （气泡）accumulate in a joint，is sharp pain and abent body-thus the name．If the bubbles form 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 too fast：whales，for example．And so，long ago，did ichthyosaurs．That these ancient sea animals got the bends can be seen from their bones．If bubbles of nitrogen form inside the bone they can 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 them selves are thus a sign that the animal once had the bends．
Bruce Rothschild of the University of Kansas knew all this when he began a study of ichthyosaur bones to find out how widespread the problem was in the past．What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150 million years．To this end，he and his colleagues traveled the world's natural-history museums，looking at hundreds of ichthyosaurs from the Triassic period and from the later Jurassic and Cretaceous periods．
When he started，he assumed that signs of the bends would be rarer in younger fossils，reflecting their gradual evolution of measures to deal with decompression．Instead，he was astonished to discover the opposite．More than 15% of Jurassic and Cretaceous ichthyosaurs had suffered the bends before they died，but not a single Triassic specimen（标本） showed evidence of that sort of injury．
If ichthyosaurs did evolve an anti-decompression means，they clearly did so quickly-and，most strangely，they lost it afterwards．But that is not what Dr Rothschild thinks happened．He suspects 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 predator （捕食动物） such as a large shark．One of the features of Jurassic oceans was an abundance of large sharks and crocodiles，both of which were fond of ichthyosaur lunches．Triassic oceans，by contrast，were mercifully shark-and crocodile-free．In the Triassic，then，ichthyosaurs were top of 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 symptom of the bends？A
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 seeB．
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'sfindingstatedinParagraph4C．
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 ichthyosaursA．
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．

分析本文属于科普说明文，主要向我们讲述了鱼龙的身体弯曲的原因以及结果．罗斯柴尔德博士通过实验推翻了以前关于鱼龙进化的一些猜测．

解答 61．A 细节理解题．根据第一段If a diver surfaces too quickly，he may suffer the bends．Nitrogen（氮） dissolved（溶解） in his blood is suddenly liberated by the reduction of pressure．可知潜水员如果露出水面太快身体会弯曲，故选A．
62．B 推理判断题．根据第三段to find out how widespread the problem was in the past和to investigate was how ichthyosaurs adapted to the problem of decompression可知罗斯柴尔德博士的研究目的是为了探讨鱼龙如何适应减压的问题，故选B．
63．C 推理判断题．根据第四段he assumed that signs of the bends would be rarer in younger fossils，接下来又说Instead，he was astonished to discover the opposite．可知，他开始时所认为的与实验得出的结论不符，因此说他的实验结果和他开始的预测相反，故选C．
64．A 推理判断题．根据第四段If ichthyosaurs did evolve an anti-decompression means…But that is not what Dr Rothschild thinks happened．可知，罗斯柴尔德博士并不认可鱼龙的抗溶解进化途径．因此A正确；误解分析：B项文章中没有提及；文章只是说they have surfaced to escape a predator，并不是说鱼龙的灭绝是鲨鱼造成的，因此C错；D项与罗斯柴尔德博士的看法正好相反；故选A．

点评做阅读理解时要快速的浏览全文，把握文章主旨大意，带着问题回到原文，寻找细节或概括相应的答案，最后要理清作者写作思路．

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