【英语阅读理解急Underproperconditions,soundwaveswillbereflectedfromahillsideorothersuchobstruction.Soundtravelsattherateofaboutone-fifthofamilepersecond.Ifthehilliselevenhundredfeetaway,ittakestwosecondsfort】

　　英语阅读理解急

　　Underproperconditions,soundwaveswillbereflectedfromahillside

　　orothersuchobstruction.Soundtravelsattherateofaboutone-fifthof

　　amilepersecond.Ifthehilliselevenhundredfeetaway,ittakestwo

　　secondsforthesoundtotraveltothehillandback.Thus,bytimingthe

　　intervalbetweenasoundanditsreflection(theecho),youcanestimatethe

　　distancetoanobstruction.

　　DuringWorldWarII,theBritishusedapracticalapplicationofthis

　　principletodetectGermanplanesontheirwaytobombLondonlongbefore

　　theenemywasnearthetarget.Theyusedradiowavesinsteadofsound

　　waves,sinceradiowavescangothroughfogandclouds.Theoutnumbered

　　RoyalAirForce(RAF)alwaysseemedtothepuzzledGermanstobelyingin

　　waitattherighttimeandneverbesurprised.Itwasradioechoesmore

　　thananythingelsethatwontheBattleofBritain.

　　Sincetheradiowaveswereusedtotellthedirectioninwhichtosend

　　theRAFplanesandthedistancetosendthem(theirrangesofflight,in

　　otherwords),thedevicewascalledradiodetectingandranging,andfrom

　　thefirstletterthewordradarwascoined.

　　6.Soundwavesreflectedfromahillcanbeusedtoestimatethe_______.

　　A)intensityofsoundB)distancetothehill

　　C)speedofsoundD)heightofthehill

　　7.DuringWorldWarTwo,theBritishused_______todetectGerman

　　planes.

　　A)aradiodetectingandrangingdeviceB)anelectronicsoundwavedevice

　　C)newelectronicinstrumentsforplanesD)newradiosetsforRAF

　　8.RadarenabledtheEnglishto________.

　　A)confuseGermanbomberpilotsB)detecttheoutnumberedRAFplaneseffectively

　　C)detectGermanplanesontheirwaytoLondonD)bothAandB

　　9.WhydidtheBritishuseradiowaves

　　A)Becausetheyweremoreexactthansoundwaves.

　　B)Becausetheycouldnotbedetected.

　　C)Becausetheywereeasiertousethansoundwaves.

　　D)Becausetheycouldgothroughfogandclouds.

　　10.Whatcanyouconcludefromthepassage

　　A)Radarwasapracticalapplicati