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
34
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.
The British used radio waves because they______.
选项
A、were more exact than sound waves
B、could not be detected
C、could penetrate fog and clouds
D、were easier to use than sound waves
答案
C
解析
从文章第二段第二句我们知道,他们(英国人)使用无线电波而不是声波是因为无线电波能够穿透云雾,所以正确答案为C;A.(无线电波)比声波更精确;B.不能被探测;D.比声波更容易使用;这三项显然不对。
转载请注明原文地址:https://kaotiyun.com/show/bkg7777K
0
大学英语四级
相关试题推荐
WhyDIY?ThereasonswhypeopleengageinDIYhavealwaysbeennumerousandcomplex.Forsome,DIYhasprovidedarareoppor
WhyDIY?ThereasonswhypeopleengageinDIYhavealwaysbeennumerousandcomplex.Forsome,DIYhasprovidedarareoppor
Itseemsyoualwaysforget—yourreadingglasseswhenyouarerushingtowork,yourcoatwhenyouaregoingtothe【11】,yourcred
Itseemsyoualwaysforget—yourreadingglasseswhenyouarerushingtowork,yourcoatwhenyouaregoingtothe【11】,yourcred
Itseemsyoualwaysforget—yourreadingglasseswhenyouarerushingtowork,yourcoatwhenyouaregoingtothe【11】,yourcred
A、Themanhassenttheordertothewomanbymistake.B、Someofthetelephonesystemsdon’tworkproperly.C、Someofthepacksd
Treesarearenewableresourcethatwhenmanagedproperlycan______ourneedsindefinitely.
A、Sheshouldfindaproperjob.B、Shecanfindanysortofjob.C、Sheshouldgotospendavacation.D、Sheshouldn’twritetoth
Iftheseclothesareproperlymerchandised,_____________(它们在圣诞节前应该相当好卖).
随机试题
函数f(χ)=2χ3-6χ2-18χ+7在区间[-2,4]上的最大值为________。
SheandI(killedanhourstrollinginthestreet).
某患者无明显不适,根据其肝右叶-右肾区超声声像图,最可能的诊断为
某建筑桩基承台如图6.8.1所示,相应于作用的基本组合时的柱轴压力F=12000kN,力矩M=1500kN.m,水平力H=600kN。承台及其上填土的平均重度为20kN/m3。按《建筑桩基技术规范》作答。试问:计算图示虚线截面处的弯矩设计值(kN.m)最接
新的工厂、生产线、新产品、新工艺是()阶段产出的可度量成果。
儿童注意的四个品质包括:注意的广度、________、________、注意的转移。
采用面向对象程序设计语言C++/Java进行系统实现时,定义类S及其子类D。D中定义方法intfun(inta,intb),这一现象称为_____________。
FrederickII’sexperimentwasviolentbecause______.Thereasonsomechildrenarebackwardinspeakingtodayisthat______.
—Readthearticleaboutthecashbasicofaccounting.—Choosethebestwordtofilleachgap,fromA,B,CorD.—Foreachquest
A、Shecouldn’tgetadmittedtoamedicalschool.B、ShedecidedtofurtherhereducationinParis.C、Aseriouseyeinfectionstop
最新回复
(
0
)