阅读理解Nooneknowswhywesleepbutit’scertainthatweneedto．Peoplewhoarepreventedfromsleepingbegintosufferobviouseffectsafterafewdays－theythinklessclearlyandtheyfall

　　阅读理解

　　Nooneknowswhywesleepbutit’scertainthatweneedto．Peoplewhoarepreventedfromsleepingbegintosufferobviouseffectsafterafewdays－theythinklessclearlyandtheyfallasleepduringtheworkinghours．

　　Therearenorulesaboutsleep．Generallyspeakinggrown-upssleepabout7andahalfhourseachnightandprobablymorethan60percentgetbetweensevenandeighthours．Butperhapseightpercentarequitehappywith5hoursorlessandfourpercentorsofindthattheywanttenhoursormore．Ifyoufeelallrightyou’reprobablygettingenoughsleep．Theimportantthingisnottoworryhowmuchotherpeopleget－theirneedsmaybedifferent．Exercisedoesn’tseemtoincreasetheneedforsleep－officeworkersforexamplesleepforaboutaslongaspeopledoingphysicallyactivework．

　　Childrensleepmorethangrown-ups－perhaps14to18hourssoonafterbirthgoingdowntogrown-uplevelsbyearlyteenage(青少年)．Sleeppatternsalsotend(倾向)tobedifferentintheoldpeoplewhomaysleeplessatnightthantheydidwhenyoungerfindsleepgettingmorebrokenandoftenmakeitaruletosleepduringthedaytime．

　　(1)

　　Somepeoplecan’tthinkclearlybecause________．

　　[]A．

　　theyhavebadmemory

　　B．

　　theyfeelsleepyduringtheworkinghours

　　C．

　　theydon’thaveenoughsleep

　　D．

　　theyarecertaintobekeptfromgoingtobed

　　(2)

　　Whetheryouhavegotenoughsleepisjudged(判断)by________．

　　[]A．

　　howmanyhoursyouhaveslept

　　B．

　　howmanyhoursyouneedtosleep

　　C．

　　ifyoudoexerciseandphysicalwork

　　D．

　　ifyoufe