yysj (第30/57页)

n　air.　Thin　air　doesn’t　hold　them　up.

    Birds　fly　he　ground　so　that　they　　see　where　they　are.　The　birds　look　for　pces　they　know.　Then　they　do　not　get　lost.　Some　birds　fly　so　low　over　the　o　that　the　waves　often　hide　them.　Many　birds　fly　a　long　distan　the　spring　and　autumn.

    Passage　28.Air

    Air　is　all　around　us.　It　is　around　us　as　we　walk　and　py.　From　the　time　we　were　born　air　is　around　us　on　every　side.　Whe　down，　it　is　around　us.　When　we　go　to　bed，　air　is　also　around　us.　We　live　in　air.　We　　live　without　food　or　water　for　a　few　days，　but　we　ot　live　for　more　than　a　few　minutes　without　air.　We　take　in　air.　When　we　are　w　or　running　we　need　more　air.　When　we　are　asleep，　we　need