阅读理解. Growingkidsneedsleep,asdopeopleofallages.Indeed,researchshowsthathealthandsafetyboth
sufferwhenwetrytogetbywithtoolittleshuteye.Soit'sfortunatethatourbodiesdosuchagoodjob
ofwaminguswhenit'stimetohitthesack.
Likehumans,otheranimalsalsotaketimeouttorest.You'veprobablyseenaliondozingatthezoo,
ormaybewatchedourdogsnoozeawaylyinginitsbed.Infact,sleepisanecessityforeveryanimalthat's
everbeenstudied.
Howlonganimalssleep,though,varieswidely.Elephantsandgiraffessleeponlyabout2to4hoursa
day,whilebatsmaynodoffforupto20hours.Duckssleeptogether,andthebirdsontheedgeofthegroup
sleepwiththeoutsideeyeopenandhalfoftheirbrainawake-probablytokeepwatchwhiletheotherhalfof
theirbrainsnoozes.Somebirdsmayevensleepwhileflying.Thefactthatallanimalsmaketimeforsleeping,
evenunderverydangeroussituations,suggeststhatsleepisveryimportant.Andindeed,somefactssuggest
thatsleepisimportantforleamingandformingpermanentmemories.
Butsleepmayalsobeprimarilyawayforanimalstosaveenergyandstayoutofharm.Thismayhelp
explainwhymeat-eatingcreaturessleepmorethanherbivores,whichareanimalsthatliveonlyonplants.
Herbivores,likecowsandzebras,needtospendmoretimesearchingforandgrazingonfoodthanmeateaters
do,suchaslionsandotherbigcats.Soabigcatmightbebetteroffsleepingforawhileafteriteats,rather
thanprowlingaroundandriskinginjury.
Butthat'sjustaguess.Scientistsneedtostudyotheranimalsaswellbeforetheycanfullyunderstandthe
benefits(好处)ofsleepandknowwhichbenefitsaremostimportantforaparticularspecies(物种).
Onethingiscertain:enoughsleepisimportanttohealthandlearning.Sogiveinwhenastrongwishto
sleephits,andcatchplentyofZZZs.1.Theunderlinedphrase"tohitthesack"means____.A.toeatsomething
B.todrinksomething
C.togetup
D.togotosleep2.From