【Youneverseehimbutthey'rewithyoueverytimeyoufly.Theyrecordwhereyouaregoinghowfastyou'retravelingandwhethereverythingonyourairplaneisfunctioningnormally.Theirabilitytowithstandalmostanydisastermakesthem】

　　Youneverseehimbutthey'rewithyoueverytimeyoufly.Theyrecordwhereyouaregoinghowfastyou'retravelingandwhethereverythingonyourairplaneisfunctioningnormally.Theirabilitytowithstandalmostanydisastermakesthemseemlikesomethingoutofacomicbook.They'reknownastheblackbox.

　　WhenplanesfallfromtheskyasaYemeniairlinerdidonitswaytoComorosIslandsintheIndiaoceanJune302009theblackboxisthebestbetforidentifyingwhatwentwrong.SowhenaFrenchsubmarine(潜水艇)detectedthedevice'shomingsignalfivedayslaterthediscoverymarkedahugesteptowarddeterminingthecauseofatragedyinwhich152passengerswerekilled.

　　In1958AustralianscientistDavidWarrendevelopedaflight-memoryrecorderthatwouldtrackbasicinformationlikealtitudeanddirection.ThatwasthefirstmodeforablackboxwhichbecamearequirementonallU.S.commercialflightsby1960.Earlymodelsoftenfailedtowithstandcrasheshoweversoin1965thedevicewascompletelyredesignedandmovedtothebackoftheplane–thearealeastsubjecttoimpact–fromitsoriginalpositioninthelandingwells(起落架舱).ThesameyeartheFederalAviationAuthorityrequiredthattheboxeswhichwereneveractuallyblackbepaintedorangeoryellowtoaidvisibility.

　　Modernairplaneshavetwoblackboxes:avoicerecorderwhichtrackspilots'conversationsandaflight-datarecorderwhichmonitorsfuellevelsenginenoisesandotheroperatingfunctionsthathelpinvestigatorsreconstructtheaircraft'sfinalmoments.Placedinaninsulated(隔绝的)caseandsurroundedbyaquarter-inch-thickpanelsofstainlesssteeltheboxescanresistmassiveforceandtemperaturesupto2000℉.Whensubmergedthey'realsoabletoemitsignalsfromdepthsof20000ft.ExpertsbelievetheboxesfromAirFranceFlight447whichcrashednearBrazilonJune12009areinwaternearlythatdeepbutstatisticssaythey'restilllikelytoturnup.Intheapproximately20deep-seacrashesoverthepast30yearsonlyoneplane'sblackboxeswereneverrecovered.

　　小题1:Whatdoestheauthorsayabouttheblackbox?A．Itensuresthenormalfunctioningofanairplane.B．Theideaforitsdesigncomesfromacomicbook.C．Itsabilit