（B）
ThesurprisingexperimentIamabouttodescribeprovesthatairisallaroundyouandthatitprovesdownuponyou.Airpressureisawonderfulforce.Whenyouswimunderwater,youcanfeelwaterpushdownyourbody.Theairallaroundyoudoesthesame.However,yourbodyissousedtoitthatyoudonotnoticethis.Thepressureiscausedbyalayerofaircalledtheatmosphere.ThislayersurroundstheEarth,extendingtoaboutfivekilometersabovetheEarth’ssurface.
Thefollowingexperimentisaneasyonethatyoucandoathome.Butmakesurethatyouaresupervised,becauseyouwillneedtousematches.Nowfoetheexperiment！
Whatyouneed
?Ahard-boiledeggwithouttheshell
?Abottlewithaneckslightlysmallerthantheegg
?Apieceofpaper
?Amatch
Metheod
1）Checkthatthepaperwillsitfirmlyontheneckofthebottle.
2）Tearthepaperintostr ipsandputthestr ipsintothebottle.
3）Lightthepaperbydroppingaburningmatchintothebottle.
4）Quicklysittheeggontheneckofthebottle.
Result
Astonishingly,theeggwillbesuckedintothebottle.Yourfriendswillbeamazedwhenyoushowthemtheexperiment.Butbecarefulwhenyouhandlematches.
Whyithappened
Asthepaperburns,itneedsoxygenandusesuptheoxygen（air）inthebottle.Theeggactsasasealintheneckofthebottle,sonomoreaircangetinside.Thisreducestheairpressureinsidethebottle.Theairpressuremustequalize,somoreairfromoutsidemustenterthebottle.Theoutsideairpressureagainsttheeggandthentheeggispushedintothebottle!Theprovesthatairisallaroundandthatitispressingdownonit.
60.Whyistheretheneedtotakecarewhenyouaredoingtheexperiment?
A.Thebottlecouldbreak.
B.Youneedtolightthepaperwithamatch.
C.Theeggneedstobeshelled.
D.Theegghastobeperfectlyplacedontheneckofthebottle.
正确答案：B
