Haveyoueverheardanechoofyourvoice?

Anechoisareflected(反射)sound.Standinaverylargeemptyhallwithnothingonthewalls.Thenshout.Thesoundsyoumakewillhitthewallsandcomebacktoyou.Thewallsreflectthesounds.Thesereflectedsoundsarecalled“echoes”.

Wecanusereflectedsoundtomakesoundtravelfarther.Holdawatchaboutfiftycentimetersfromyourear.Youcannothearit.Thesoundofthewatchtravelsashortwayinalldirections.Itdoesnottravelasfarasyourear.Youcanmakeittraveltoyourearbyusingarollofcardboard(纸板筒).

Maketherollofcardboardaboutfiftycentimeterslong.Putoneendoveryourearandholdthewatchattheother.Nowyoucanhearthewatchbecausethesoundhasnotgoneinalldirections.Itisreflecteddowntherolltoyourear.

Amegaphone(喇叭筒)worksinthesameway.Itmakessoundtravelfarther.Itreflectsthesoundintoabeamwhichcantravelalongway.Intheshipthesailorusesthemegaphonetomakehisvoicetravel.Withoutthemegaphonehisvoicecannottravelfar.

Weusereflectedsoundinmanyways.Weuseittomeasurethedepthoftheseaforexample.Amongtheanimalsbatsandwhalesusereflectedsoundtotellthemwheretheyareandwhatthingsarenearthem.

小题1:Whichistherightorderofhearingourechoinaverylargeemptyhall?

a.Wehearthereflectedsound b.Thesoundreturnstous

c.Thesoundhitsthewalls d.WemakeasoundA．cbadB．cabdC．dcbaD．dbca小题2:.Fromthetextwelearnthat__________.A．reflectedsoundisusefulonlytoblindpeopleB．peoplehaven’tmadeuseofreflectedsoundyetC．batsusereflectedsoundtoflyandgetfoodD．whalesdon’tusereflectedsoundastheyliveinthesea小题3:Ifyouhaven’tgotamegaphone____willhelpyoutomakeyourvoicetravelfarther.A．alongpieceofwoodB．arollofcardboardC．athinthreadD．alongpieceofsilk