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
23
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 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 e- valve 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 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 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 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 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 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
答案
B
解析
本题是一个推断题。考察考生对文章结构的理解。
转载请注明原文地址:https://kaotiyun.com/show/NMDd777K
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
Whatisthefirstjobthemanappliedforrightafterhisuniversitygraduation?ThecompanyemployednotonlyBritishtourgui
DoesthepublisherofDouglasStarr’sexcellentBlood—AnEpicHistoryofMedicineandCommerceactuallyexpecttosellmanycopi
WhoearnslessintheUnitedStatesthanthoseinmanyindustrializedcountries?
A、Balloonsareeasiertolift.B、Itisagoodtimeforexercise.C、Thevisibilityisgood.D、Thereisnodangerinflying.C
Whenamagazineforhigh-schoolstudentsaskeditsreaderswhatlifewouldbelikeintwentyyears,theysaid:machineswouldbe
Amultinationalcorporationisacorporateenterprise,whichthoughheadquarteredinonecountry,conductsitsoperationsthroug
NewfiguresfromFrance,GermanyandItaly--thethreebiggesteconomiesinthe12-countryEurozone-suggestthecontinent’sec
Weholdsthesetruthstobeselfevidentthat______.
WhatisCathyfedupwith?______onpackingcases
Australia
随机试题
陈某财产被张某、赵某非法侵占,向法院提起自诉,由于陈某与赵某有亲戚关系,仅起诉张某,法院受理。关于本案说法正确的是:()
气顶监测井主要用来定期监测气顶压力,了解气顶受挤压和扩张情况。()
证明函数f(x)=ln(x+)为奇函数.
如果物资验收入库的同时支付货款,则通过“应付账款”账户核算。如果物资验收入库后仍未付款,则按发票账单金额通过银行存款核算。()
产品质量法中的产品,是指经过加工、制作,用于销售的产品,但()不适用该法规定。
在《论十大关系》中,毛泽东提出要处理好若干关系,表明他实际上思考了如何开辟一条与苏联不同的中国工业化道路。这些关系主要有()。
气候系统是一个包括()、陆地表面等在内的,能够决定气候形成、气候分布和气候变化的统一的物理系统。
根据我国两审终审制度,一个案件经过两级法院审判后当事人就不能对判决、裁定提出异议。()
①此事赢得光绪皇帝支持②西苑铁路建成后,慈禧太后可以随时从紫光阁站乘坐小火车游览北海,然后到镜清斋休息③光绪十二年(1886年),皇城御苑中的铁路开始动工,起点在中海的瀛秀园,终点在北海镜清斋(后改名为静心斋),全长1510.4米,光绪十四年(1888
[*]
最新回复
(
0
)