machines.B.Itneverchangesposition.C.ItfloatsslowlyaroundtheEarth.D.Itmaycauseproblemsforspaceshuttles.答案:D 细节理解题。根据第四段的句子:Themajorproblemwiththespacetrashisthatitmayhitworkingsatellitesanddamagetravelingspaceship.Moreover,piecesofjunkmaycrashwitheachotherandbreakintopieceswhichfallbacktotheEarth.可知太空垃圾会给太空飞船带来很多问题。D项的表述正确,故选D。4.Whathasbeendoneaboutthespacetrashproblem?A.Scientistshavecleanedupmostofthetrash.B.Largepiecesofspacetrasharebeingcloselywatched.C.Manynationshaveworkedtogethertostoppollutingspace.D.Groundstationsarebuilttohelpstorethetrashproperlyinspace.答案:B 细节理解题。根据第四段的句子:Toavoidthis,scientistshaveinventedseveralwaysforclearingthesky.Groundstationshavebeenbuilttomonitorlargerpiecesofspacetrashtopreventthemfromcrashingintoworkingsatellitesorspaceshuttles.可知现阶段比较大的太空废物正在被紧密监测,故选B。
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