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
Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for many ye
Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for many ye
admin
2008-11-13
50
问题
Why don’t birds get lost on their long flights from one place to another? Scientists have puzzled over this question for many years. Now they’re beginning to fill in the blanks.
Not long ago, experiments showed that birds rely on the sun to guide them during daylight hours. But what about birds that fly by night? Tests with artificial stars have proved that certain night-flying birds are able to follow the stars in their long-distance flights.
A dove (鸽子)had spent its lifetime in a cage and had never flown under a natural sky. Yet it showed an inborn ability to use the stars for guidance. The bird’s cage was placed under an artificial star-filled sky. (76)
The bird tried to fly in the same direction as that taken by his outdoor cousins.
Any change in the position of the artificial stars caused a change in the direction of his flight.
(77)
But the stars are apparently their principal means of navigation(航行)only.
When the stars are hidden by clouds, they seemingly find their way by such landmarks as mountain ranges, coast lines, and river courses. But when it’s too dark to see these, the doves circle helplessly, unable to find their way.
选项
A、have been known to scientists for many years
B、have only recently been discovered
C、are known by us
D、will probably remain a mystery
答案
B
解析
见第一段中句子“Scientists have puzzled over this question for many years.Now they’re beginning to fill in the blanks.”。
转载请注明原文地址:https://kaotiyun.com/show/KePO777K
0
成人本科学位英语
相关试题推荐
Moreandmore,theoperationsofourbusinesses,governments,andfinancialinstitutionsarecontrolledbyinformationthatexis
Thereareseveralstepsthatcanbetaken,ofwhichthechiefoneistodemandofalltheorganizationsthatexistwiththedecl
Thepoliceaccusedhimofsettingfiretothebuildingbuthedenied______intheareaonthenightofthefire.
Whilefashionisthoughtofusuallyinrelationtoclothing,itisimportanttorealizethatitcoversamuchwiderdomain.Iti
TheUnitedStatesiswell-knownforitsnetworkofmajorhighwaysdesignedtohelpadrivergetfromoneplacetoanotherinthe
AlthoughtheAmericancivilizationtookoverandreplacedthefrontieroveracenturyago,theheritageofthefrontierisstill
Yourcollegestudentsaremenofprivilege.Itcoststentimes______,inlabourandcareandmoney,tobringyououtwhereyoua
Thedrugstoreatthecornerofourstreetsellsaspirinsandpenicillinprescriptions.
Stupidpeopleoftenfinditdifficultto________theirprejudices.
Theinterviewershouldtakedownnotesatthemomenttheperson_________answersthequestions.
随机试题
简述普萘洛尔的降压机制。
有一台两极发电机,电枢的直径d=0.2m,长度l=0.4m,固定在它上面的矩形线圈的匝数N=20,气隙中的磁场是按正弦分布的,磁感应强度最大值BmA=1Wb/m2,若电枢以恒定转速n=3000r/min在此磁场中转动,求电动势的最大值及时间时的瞬时值是多少
恒电位仪输出电流、电压值逐渐降低,电位测量表控制电位、通电点电位不变,管线保护长度缩短,可能的原因是()。
目前普遍使用的氟化凝胶的含氟成分是氟化凝胶不适用于
背景资料:某水利枢纽工程项目包括大坝、水电站等建筑物。在水电站厂房工程施工期间发生如下事件:事件一:施工单位提交的施工安全技术措施部分内容如下:(1)爆破作业,必须统一指挥,统一信号,划定安全警戒区,并明确安全警戒人员。在引爆时,无关人员一律退到安全
甲向售货员乙询问某商品的价格,乙反问:“你愿意出多少钱购买?”此时乙向甲作出的是要约邀请()
根据《立法法》的规定,下列事项中,设区的市、自治州的人民政府有权制定地方政府规章的有()。
下列不属于明暗素描中三个基本层次的是()。
中国无产阶级除了具有与先进生产方式相联系、没有私人占有的生产资料、富于组织纪律性等一般无产阶级的基本优点外,还具有自身的优点和特点。下列选项中,属于中国无产阶级自身的优点和特点的有()。①中国无产阶级具有坚决的斗争性②中国无产阶级分布集中③
Thecompanyhadtoputforwarda(propose)______thatlay-offs(下岗)beconsidered.
最新回复
(
0
)