首页
外语
计算机
考研
公务员
职业资格
财经
工程
司法
医学
专升本
自考
实用职业技能
登录
外语
The fossil remains of the first flying vertebrates, the pterosaurs. have intrigued paleontologists for more than two centuries,
The fossil remains of the first flying vertebrates, the pterosaurs. have intrigued paleontologists for more than two centuries,
admin
2010-07-06
38
问题
The fossil remains of the first flying vertebrates, the pterosaurs. have intrigued paleontologists for more than two centuries, How such large creatures, which weighed in some eases 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 wing like 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 ail 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 hats 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 warm-blooded because flying implies a high rate of metabolism, which in turn implies a high internal temperature. Huxley 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 hair—like 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 them- selves by jumping from cliffs, by dropping from trees or even by rising into light winds from the surfaces of waves Each hypothesis has its difficulties. The first wrongly assumes that the pterosaurs’ hind feet resembled a hat’s and could serve as hooks by which the animal could hang in preparation for flight. The second hypothesis seems unlikely 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.
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 in- formation.
C、Three hypotheses are outlined, and evidence supporting each is given,
D、Recent discoveries are described, and their implications for future study are projected.
答案
B
解析
分析推理题。文章最后二段首先是提出几种假设,然后进行了否定,并说明了否定的原因,因此其结构特点是B :提出假设→逐→驳斥。
转载请注明原文地址:https://kaotiyun.com/show/ZYDd777K
本试题收录于:
公共英语四级笔试题库公共英语(PETS)分类
0
公共英语四级笔试
公共英语(PETS)
相关试题推荐
WhatarethetwoseasoningsusedbymostAmericans?
Althoughtherehadbeenvarioussmallcamerasdeveloped,itwasnotuntilGeorgeEastmanintroducedtheKodakin1888thatthem
Forcenturies,explorershaveriskedtheirlivesventuringintotheunknownforreasonsthatweretovaryingdegreeseconomican
【B1】Swedenhasgotapopulationofonly8million,butitisalargecountrywithanareaof450,000squarekilometers.【B2】The
【B1】Swedenhasgotapopulationofonly8million,butitisalargecountrywithanareaof450,000squarekilometers.【B2】The
Predictionsofmanyrobotsinindustryhaveyetcometrue.Fortenyearsormore,manufacturersofbigrobotshaveexplainedhow
Althoughtherehadbeenvarioussmallcamerasdeveloped,itwasnotuntilGeorgeEastmanintroducedtheKodakin1888thatt
Allthewisdomoftheages,allthestoriesthathavedelightedmankindforcenturies,areeasilyandcheaply【21】______toal
Allthewisdomoftheages,allthestoriesthathavedelightedmankindforcenturies,areeasilyandcheaply【21】______toal
随机试题
从以下五个选项中选择正确一个正确答案填空:A.密度增高B.高信号C.液性暗区D.HU为0E.浓聚CT上纯水的CT值()
已知的值等于_______.
高速公路的交叉路口全部采用平面交叉公路。()
A.磷酸甘油酸激酶B.烯醇化酶C.丙酮酸激酶D.丙酮酸脱氢酶复合体E.丙酮酸羧化酶糖异生途径的关键酶
女孩,2岁,体检闻及胸骨左缘第2~3肋间Ⅱ~Ⅲ级收缩期杂音,肺动脉瓣区第2音亢进,伴固定性分裂。该患儿的诊断是
题中所说的展览品在进出境过程中的特点有()。深圳联合公司在展览会结束后,将该批货物运输出境,核销结关,下列说法中正确的是()。
根据税收征收管理法律制度的规定,下列各项中,不符合规定的是()。
中国公民出入境管理工作中不包括对华侨、港澳台同胞的管理。()
差别阈限及其操作定义
Youcannotfinishthetermpaperontimebecauseyoujoinedtheschool-organizedfieldpracticeprograminGuangzhouinthesumm
最新回复
(
0
)