It'sgettinglate.You'retryingtofinishabook.Butyoureyesstarttofeelvery1.Onlytwomorepagestogountil...zzzzzzzzzzzzz.

Sleepingispartofournaturaldailyrhythm.Oureyesclose,ourbodiesrelax.Wedonot2tolightornoise.Everythingaboutusseemstoslowdown.Everything,thatis,exceptourbrains.Howdoscientistsknowthis?Scientistsusespecialwiresandmachinestostudybrainactivityduringsleep.Theyattachaspecialmachinetosleepingpatients.Thismachine3brainwaves.

Scientistsfoundthatthereareseveralstagesofsleep.Duringonestageofsleep,calledREMsleep(rapideyemovementsleep),ourDramscanbeasactiveastheyarewhenweareawake.We4havethreetofiveperiods(片段)ofREMsleeppernight.Thisiswhenwehavemostofourdreams.

Surprisingly,scientistsdon'tknowexactly5wesleep.However,theyhavesomegoodideas.Manypeoplethinkthatsleepinggivesourbodya“time-out”soitcanrepairandbuilditself.Somechemicalsthatmakeyougrowarereleasedwhenyousleep.Otherchemicalsthathelpyoufightdiseasearealsomoreactivewhenyourest.

Sleepingmayalsobeimportantfor6.Somestudiesshowthatpeoplerememberthingsbetterafterthey"sleeponit."Inmostcases,youwakeupinthemorningfeelingrestedandrefreshed.Thatis,unlessyou'vehadaterribledream.7,yourheartmaystillbepounding(砰砰跳)fromanightmare(恶梦).

A

warm

B

heavy

C

narrow

D

dry

A

lookforward

B

payattention

C

doharm

D

giveresponse

A

records

B

attracts

C

causes

D

requires

A

hardly

B

nearly

C

usually

D

especially

A

how

B

why

C

where

D

when

A

driving

B

writing

C

learning

D

playing

A

Atmost

B

Atlast

C

Inaddition

D

Infa