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  3. The fossil remains of the first flying vertebrates, the pterosaurs, have int

The fossil remains of the first flying vertebrates, the pterosaurs, have int

游客2024-01-13  34
问题     The fossil remains of the first flying vertebrates, the pterosaurs, have intrigued paleontologists lor more than two centuries. How such large crea- tures, which weighed in some cases as much as a piloted hang-glider and had wingspans from 8 to 12 meters, solved the problems of powered flight, and exactly what these creatures were—reptiles or birds—are among the questions scientists have puzzled over.
    Perhaps the least controversial assertion about the pterosaurs is that they were reptiles. Their skulls, pelvises, and hind feet are reptilian. The anatomy of their wings suggests that they did not evolve into the class of birds. In pterosaurs a greatly elongated fourth finger of each forelimb supported a winglike membrane. The other fingers were short and reptilian, with sharp claws. In birds the second finger is the principal strut of the wing, which consists primarily of feathers. If the pterosaurs walked on all fours, the three short fingers may have been employed for grasping. When a pterosaur walked or remained stationary, the fourth finger, and with it the wing, could only turn upward in an extended inverted V-shape along each side of the animal’ s body.
    The pterosaurs resembled both birds and bats in their overall structure and proportions. This is not surprising because the design of any flying vertebrate is subject to aerodynamic constraints. Both the pterosaurs and the birds have hollow bones, a feature that represents a savings in weight. In the birds, however, these bones are reinforced more massively by internal struts.
    Although scales typically cover reptiles, the pterosaurs probably had hairy coats. T. H. Huxley reasoned that flying vertebrates must have been warmblooded because flying implies a high rate of metabolism, which in turn implies a high internal temperature. Hux- ley speculated that a coat of hair would insulate against loss of body heat and might streamline the body to reduce drag in flight. The recent discovery of a pterosaur specimen covered in long, dense, and relatively thick hairlike fossil material was the first clear evidence that his reasoning was correct.
    Efforts to explain how the pterosaurs became airborne have led to suggestions that they launched themselves by jumping from cliffs, by dropping from trees, or even by rising into light winds from the crests of waves. Each hypothesis has its difficulties. The first wrongly assumes that the pterosaurs’ hind feet resembled a bat’s and could serve as hooks by which the animal could hang in preparation for flight. The second hypothesis seems un- likely because large pterosaurs could not have landed in trees without damaging their wings. The third calls for high waves to channel updrafts. The wind that made such waves however, might have been too strong for the pterosaurs to control their flight once airborne. [br] Which of the following best describes the organization of the last paragraph of the passage?
选项 A、New evidence is introduced to support a traditional point of view.
B、Three explanations for a phenomenon are presented, and each is disputed by means of specific information.
C、Three hypotheses are outlined, and evidence supporting each is given.
D、Recent discoveries are described, and their implications for future study are projected.
E、A summary of the material in the preceding paragraphs is presented, and conclusions are drawn.
答案 B
解析 文章最后一段的结构：注意：organization实际上是问在这一段中作者写了哪些内容。A．给出支持一传统观念的新证据。无。B．对一个现象给了三个解释，每一个都被一些证据否定了。正确。符合最后一段的内容。C．给出三个假设，并给出支持每一个的证据。和原文态度相反。D．描写最近发现和预测它们对将来研究的意义。无。E．总结前几段的资料，并下结论。无。
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