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 （氣泡）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（減壓） 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（標(biāo)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 （捕食動(dòng)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（獵物） 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 本文屬于科普說明文，主要向我們講述了魚龍的身體彎曲的原因以及結(jié)果． 羅斯柴爾德博士通過實(shí)驗(yàn)推翻了以前關(guān)于魚龍進(jìn)化的一些猜測(cè)．

解答 61．A  細(xì)節(jié)理解題．根據(jù)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．可知潛水員如果露出水面太快身體會(huì)彎曲，故選A．
62．B  推理判斷題．根據(jù)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可知羅斯柴爾德博士的研究目的是為了探討魚龍如何適應(yīng)減壓的問題，故選B．
63．C  推理判斷題．根據(jù)第四段he assumed that signs of the bends would be rarer in younger fossils，接下來又說Instead，he was astonished to discover the opposite．可知，他開始時(shí)所認(rèn)為的與實(shí)驗(yàn)得出的結(jié)論不符，因此說他的實(shí)驗(yàn)結(jié)果和他開始的預(yù)測(cè)相反，故選C．
64．A  推理判斷題．根據(jù)第四段If ichthyosaurs did evolve an anti-decompression means…But that is not what Dr Rothschild thinks happened．可知，羅斯柴爾德博士并不認(rèn)可魚龍的抗溶解進(jìn)化途徑．因此A正確；誤解分析：B項(xiàng)文章中沒有提及；文章只是說they have surfaced to escape a predator，并不是說魚龍的滅絕是鯊魚造成的，因此C錯(cuò)；D項(xiàng)與羅斯柴爾德博士的看法正好相反；故選A．

點(diǎn)評(píng) 做閱讀理解時(shí)要快速的瀏覽全文，把握文章主旨大意，帶著問題回到原文，尋找細(xì)節(jié)或概括相應(yīng)的答案，最后要理清作者寫作思路．

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