阅读理解阅读理解

阅读下列短文，从各题所给的A、B、C、D四个选项中，选出最佳选项。

Asaresultofpollution,LakeErie,onthebordersoftheU.S.A.andCanada,isnowwithoutmanylivingthings.

Pollutioninwaterisnotsimplyamatterof“poisons”killinglargenumbersoffishovernight.Veryoftentheeffectsofpollutionarenotnoticedformanymonthsoryearsbecausethefirstorganisms(生物体)tobeaffectedareeitherplantsorplankton(浮游生物).Theseorganismsarethefoodoffish,birds,andothercreatures.Whenthisfooddisappears,thefishandbirdsdietoo.Inthiswayawholefoodchaincanbewipedout,anditisnotuntildeadfishandwaterbirdsareseenattheriver'sedgeorontheseashorethatpeoplerealizewhatishappening.

Wheredothesubstanceswhichpollutethewatercomefrom?Therearetwomainsources;sewage(污水)andindustrialwaste.Asmoredetergent(洗涤剂)isusedinthehomes,somoreofitisfinallyputintoourrivers,lakesandseas.Detergentsharmwaterbirdsbreakingdownthenaturalsubstanceswhichkeeptheirfeatherswaterproof.Sewageitself,ifnotproperlytreated,makesthewaterdirtyandpreventsallformsoflifeinriversandtheseafromreceivingtheoxygentheyneed.Industrialwasteisevenmoreharmfulsincetherearemanyhighlypoisonousmaterialsinit,suchascopperandlead.

So,ifwewanttostopthispollution,theanswerissimple.Sewageandindustrialwastemustbemadecleanbeforeflowingintothewaterreservoirs.Itmayalreadybetoolatetosavesomeriversandlakes,butotherscanstillbesavedifthecorrectactionistakenatonce.

1．Pollutioninwaterisnoticed________.

[]

A．whenthefirstorganismsareaffected.

B．whenagreatmanyfishandbirdsdie

C．whenpoisonsarepouredintowater

D．assoonasthebalanceofnatureisdestroyed

2．Thelivingthingsdiebecausethereisno________inthelakeorriver.

[]

A．oxygenB．poisonC．waterD．fish3．Whatisthemeaningof“waterproof”,theunderlinedwordinthethirdparagraph?

[]

A．fullofwater

B．coveredwithwater

C．notallowingwatertogothrough

D．cleanedbywater

4．Thewaytostopwaterpollutionis________.

[]

A．topu