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
Under proper conditions, sound waves will be reflected from a hillside or other such obstruction. Sound travels at the rate of a
Under proper conditions, sound waves will be reflected from a hillside or other such obstruction. Sound travels at the rate of a
admin
2013-05-19
26
问题
Under proper conditions, sound waves will be reflected from a hillside or other such obstruction. Sound travels at the rate of about one-fifth of a mile per second. If the hill is eleven hundred feet away, it takes two seconds for the sound to travel to the hill and back. Thus, by timing the interval between a sound and its reflection (the echo), you can estimate the distance to an obstruction.
During World War I1 the British used a practical application of this principle to detect German planes on their way to bomb London before the enemy was near the target. They used radio waves instead of sound waves, since radio waves can penetrate fog and clouds. The outnumbered Royal Air Force (RAF) always seemed to the puzzled Germans to be lying in wait at the right time and never to be surprised (袭击). It was radio echoes more than anything else that won the Battle of Britain.
Since the radio waves were used to tell the direction in which to send the RAF planes and distance to send them ( their range of flight, in other words), the device was called radio directing and ranging, and from the initials the word radar was coined.
Radar enabled the English ______.
选项
A、detect German planes on their way to London
B、direct the outnumbered RAF planes effectively
C、confuse German bomber pilots
D、both A and B
答案
A
解析
从文章第二段第一句我们知道,在二战期间,英国人运用这一原理来探测敌人接近目标之前到伦敦的距离,这里所说的实际运用这一原理就是指雷达,所以正确答案为A;B.有效地指挥数量上占优越的皇家飞机,这也不对的,雷达可以探测敌机距离,但是人运用它来指挥飞机;C.迷惑德国轰炸机飞行员,这也不对,雷达没有这个功能;D.把A和B两项放在一起不符原文。
转载请注明原文地址:https://kaotiyun.com/show/Ikg7777K
0
大学英语四级
相关试题推荐
WhyDIY?ThereasonswhypeopleengageinDIYhavealwaysbeennumerousandcomplex.Forsome,DIYhasprovidedarareoppor
Japanisgettingtoughaboutrecycling—andnotinthepaperandplastickindofway.Recently,thecountryrequiresthatallele
Japanisgettingtoughaboutrecycling—andnotinthepaperandplastickindofway.Recently,thecountryrequiresthatallele
Itseemsyoualwaysforget—yourreadingglasseswhenyouarerushingtowork,yourcoatwhenyouaregoingtothe【11】,yourcred
The__________oftherelieftothefloodedareawasheldupbecauseoftheinconvenientroadconditions.
Treesarearenewableresourcethatwhenmanagedproperlycan______ourneedsindefinitely.
Ifanymanheredoesnotagreewithme,heshould______hisownplanforimprovingthelivingconditionsofthesepeople.
A、Childrenrearedunderaverageconditionspossessaverageintelligence.B、Lackofopportunitypreventsthegrowthofintelligen
A、Hisstorieswereinspiredbyhistravels,B、Histravelspreventedhimfromwriting.C、Hetraveledinordertorelaxfromthep
随机试题
刚性矩形基础如图示,经计算发现基底右侧出现拉力,为使基底不出现拉力,下列哪种措施是有效的?
特种设备检测技术中,()的目的是测出构件受载后表面的或内部各点的真实应力状态。
为了适应城市交通迅速发展的需要,为缓解城市交通拥堵的矛盾,大中城市开始落实“优先发展城市公共交通的战略”规划,并逐步完善综合交通系统和建设新的交通设施,主要表现在()
下列情形中,可以引起诉讼时效中断的有()。
我国海运保险的几种基本险别中,承保责任范围最狭窄的是()。
导游人员送旅游者乘火车、轮船离站,应提前()分钟到达车站码头。
人的自由其实不过是“戴着镣铐的舞蹈”。()
数据的预处理包括哪些内容?
(2013上项管)项目经理在5月1日对一个软件开发项目进行了挣值分析,项目CPI是1.0,进度偏差为零。在6月3日,附近的河流泛滥,致使开发计算机机房被淹,导致所有工作停工2周时间,该项目遭受了______。
CompletetheStudentProfilebelow.UseNOMORETHANTHREEWORDSORANUMBERforeachanswer.STUDENTPROFILE-GRISHAMCO
最新回复
(
0
)