14．If a diver surfaces（浮出水面） too quickly，he may suffer the bends（減壓病）．Nitrogen （氮） dissolved （溶解） in his blood is suddenly liberated（釋放）by the reduction of pressure．The consequence，if the bubbles （氣泡） accumulate in a joint，is sharp pain and a bent 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（魚龍）．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 themselves 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 150million years．To this end，he and his colleagues traveled the world's natural-history museums，looking at hundreds of ichthyosaurs from the Triassic（三疊紀(jì)） period and from the later Jurassic（侏羅紀(jì)） and Cretaceous（白堊紀(jì)） periods．
When he started，he assumed that signs of the bends would be rarer in younger fossils，reflecting their gradual evolution（進(jìn)化）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．
58．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．
59．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
60．Rothschild's finding stated in Paragraph 4C．
A．confirmed his assumption
B．speeded up his research process
C．disagreed with his assumption
D．changed his research objectives
61．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 科普知識(shí)類文章．文章主要介紹Rothschild教授關(guān)于魚龍類生物在近1億5千萬(wàn)年里如何適應(yīng)減壓?jiǎn)栴}的研究．在開(kāi)始研究時(shí)，他原本認(rèn)為年輕化石里彎曲的跡象會(huì)比老化石里的少，因?yàn)檫@標(biāo)志著魚龍類生物逐漸進(jìn)化出反減壓器官，然而他的研究結(jié)果得出相反的結(jié)論．
解答 58-61 ABCA
58．選A 細(xì)節(jié)理解題．第一段第三句提到遭遇bend的癥狀是"sharp pain and a bent body"，此處bent等于twisted，意為"扭曲的，彎曲的"．故答案選A．
59．選B 細(xì)節(jié)理解題．根據(jù)第三段第二句"What he particularly wanted to investigate was how ichthyosaurs adapted to the problem of decompression over the 150million years．．"可知Rothschild教授的研究目的是如何適應(yīng)減壓?jiǎn)栴}，答案為B．
60．選C 細(xì)節(jié)理解題．根據(jù)第四段第二句"Instead，he was astonished to discover the opposite．"可知研究結(jié)果與他原本的假設(shè)相反，因此答案為C．
61．選A 推理判斷題．根據(jù)文章倒數(shù)第二段第一句If ichthyosaurs did evolve an anti-decompression means，they clearly did so quickly-and，most strangely，they lost it afterwards．可以推斷出答案．Rothschild可能已經(jīng)得出結(jié)論：魚龍類生物未能進(jìn)化出反減壓器官．
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