第8题：C、
 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 knewall 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 andCretaceous 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 andCretaceous 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 whatDr 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 andCretaceous, they were prey(猎物) as well as predator—and often had to make a speedy exit as a result. Rothschild’sfindingstatedinParagraph4 .A．confirmed his assumption
B、speeded up hisresearch process
C．disagreed with his assumption
D．changed his research objectives
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I与碱石灰共热可转化为立方烷，立方烷的核磁共振氢谱中有{{U}} {{/U}}个峰。
A．
