判断正误Lighttravelsataspeedwhichisaboutamilliontimes急.
TheSpeedofLight
Lighttravelsataspeedwhichisaboutamilliontimesfasterthanthespeedofsound.
Inonesecond,lighttravelsabout300,000kilometres.
Butsoundtravelsonly0.344kilometres.Youcangetsomeideaofthisdifferencebywatchingthestartofarace.Ifyou
Standsomedistance(距离)awayfromthestarter,youcanseesmokecomefromhisgun
(枪)beforethesoundreachesyourears.
Thisgreatspeedoflightproducessomestrangefacts.Sunlighttakesabout8minutesto
reachus.Ifyoulookatthelightofthemoontonight,rememberthatthelightleftthemoon1.3secondbeforetheyreachedyou.Theneareststarisfarawayfromtheearth.Thelightwhichyoucanseefromittonightstartedtotraveltowardsyoufouryearsagoataspeedofnearly2millionkilometersoneminute.Insomecases(情况)thelightfromoneoftonight’sstartsstartedonitsjourneytoyoubeforeyouwereborn.
Ifwewanttobehonest(诚实),wecannotsay“Thestarsareshiningtonight.”Wehavetosay,“Thestarslookpretty(漂亮).Theywereshiningfouryearsago.Buttheirlighthasonlyjustreachedtheearth..”
判断正误：
（）1.Lightspeedisaboutamilliontimesfasterthansoundspeed.
（）2.Ifyoustand100metresawayfromastarter,youcanhearthegunbeforeyouseethesmoke.
()3.Themoonmustbeabouttwomillionkilometersawayfromtheearth.
()4.Thesunmustbeabout480times300,000kilometresawayfromtheearth..
()5.Themoonlightweseetonightstartedtotraveltowardsusfouryearsago.
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