一篇任务型DidyousleepthedayawayonMarch21?WellyoushouldhavedonethatbecauseitwasWorldSleepingDay.Thisistheonedayoftheyearwhenpeoplearoundtheworldcareabouttheirsleepandaskthemselvesalotofquestionsaboutsleep.Whydoweneedsleep?Nobodyasyetcangiveaperfectanswertothisquestion.However,testshaveshownthatlack(缺少)ofsleepoveraboutfourweeksleadstoastrongdropinbodytemperature,greatweightlossandfinallysickness.Differentpeopleneeddifferentamountsofsleep.Eighthoursanightisconsideredtheaverageamountofsleep.Forteenagerstheleastnumberofsleepinghoursadvisedbydoctorsaretenhoursforprimaryschoolstudents,nineforjuniorhighsandeightforseniorhighs.Somepeopleseemtogetalongjustfinewithverylittlesleepatnight.LeadingAmericanscientistThomasEdisonsaidthatsleepwasawasteoftime.Hedid,however,takenapsduringtheday.Ontheotherhand.AlbertEinstein,anothergreatscientist,saidheneededatleasttenhours'sleepanight.Herearesomeofthemostusefulsuggestions,foragoodnight'ssleep:Gotobedatthesametime.Useyourbedonlytosleep.Don'texerciseintheevening.Keepthebedroomdarkandquiet.Drinkaglassofmilkbeforesleep.Stoplookingatthewatchwhileyoucan'tsleep!