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
64
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
Peoplemayspendtimeinmakingdecisionsabout______.Thebesttitleforthispassageis
WhatarethetwoseasoningsusedbymostAmericans?
PursuingfreetradethroughWTOhasmanyattractions.Countriesbindthemselvesandtheirtradingpartnerstotransparentandno
Predictionsofmanyrobotsinindustryhaveyetcometrue.Fortenyearsormore,manufacturersofbigrobotshaveexplainedhow
Predictionsofmanyrobotsinindustryhaveyetcometrue.Fortenyearsormore,manufacturersofbigrobotshaveexplainedhow
Predictionsofmanyrobotsinindustryhaveyetcometrue.Fortenyearsormore,manufacturersofbigrobotshaveexplainedhow
Predictionsofmanyrobotsinindustryhaveyetcometrue.Fortenyearsormore,manufacturersofbigrobotshaveexplainedhow
Predictionsofmanyrobotsinindustryhaveyetcometrue.Fortenyearsormore,manufacturersofbigrobotshaveexplainedhow
Althoughtherehadbeenvarioussmallcamerasdeveloped,itwasnotuntilGeorgeEastmanintroducedtheKodakin1888thatt
Althoughtherehadbeenvarioussmallcamerasdeveloped,itwasnotuntilGeorgeEastmanintroducedtheKodakin1888thatt
随机试题
球壳板焊缝立焊表面层时应采用()运条法。
下列属于内耳结构的是【】
以下有一项不是影响口腔生态系的物理化学因素
理想盖髓剂应具备性质如下,除外
正常成人腋测法体温应是
下列关于诉讼时效中断的相关说法中,不正确的是()。
在保证合同中,当事人约定了保证范围和保证期间,但当事人对保证方式没有约定的情况下,下列关于保证人责任的表述正确的是__________。
[*]
阅读以下程序:#includemain(){intcase;floatpfintF;printf("请输入2个数:");scanf("%d%f",&case,&printF);
设一棵树的度为3,其中没有度为2的结点,且叶子结点数为6。该树中度为3的结点数为
最新回复
(
0
)