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                                            Electr icity

Themodernageisanageofelectr icity,Peoplearesousedtoelectr iclights,radio,televisionsandtelephonesthatitishardtoimaginewhatlifewouldbelikewithoutthem.Whenthereisapowerfailure,peoplegropeaboutinflickeringcandlelight,

carshesitateinthestr eetsbecausetherearenotr afficlightstoguidethem,andfoodspoilsinsilentr efrigerators.Yet,peoplebegantounderstandhowelectr icityworksonlyalittlemorethantwocenturiesago.Naturehasapparentlybeen

experimentinginthisfieldformillionsofyears.Scientistsarediscoveringmoreandmorethatthelivingworldmayhold

manyinterestingsecretsofelectr icitythatcouldbenefithumanity.

Alllivingcellssendouttinypulsesofelectr icity.Astheheartbeats,itsendsoutpulsesofrecord;theyformanelectr ocardiogram,whichadoctorcanstudytodeterminehowwelltheheartisworking.Thebrain,too,sendsoutbrainwavesofelectr icity,whichcanberecordedinanelectr on-cephalogram.Theelectr iccurrentsgeneratedbymostlivingcellsareextr emelysmall-oftensosmallthatsensitiveinstr umentsareneededtorecordthem.Butinsomeanimals,certainmusclecellshavebecomesospecializedaselectr icalgeneratorsthattheydonotworkasmusclecellsatall.Whenlargenumbersofthesecellsare

linkedtogether,theeffectscanbeastonishing.

Theelectr iceelisanamazingstoragebattery.Itcansendajoltofasmuchaseighthundredvoltsofelectr icitythroughthe

waterinwhichitlives.Anelectr ichousecurrentisonlyonehundredtwentyvolts)Asmanyasfourfifthsofallthecellsintheelectr iceel'sbodyarespecializedforgeneratingelectr icity,andthestr engthoftheshockitcandelivercorrespondsroughly

tothelengthofitsbody.

【单选】

Whatisthemainideaofthepassage?

Electr iceelsarepotentiallydangerous

Biologyandelectr icityappeartobecloselyrelated

Peoplewouldbeatalosswithoutelectr icity

Scientistsstillhavemuchtodiscoveraboutelectr ic

答案及解析：统观全文可知,文章用了大量的篇幅介绍生物和电流的密切关系。