【新概念英语第53课HotSnake.Abirdhadsnatchedupthesnakefromtheground.为什么要用过去完成全文内容AtlastfiremenhaveputoutabigforestfireinCalifornia.Sincethen,theyhavebeentryingtofindouthowthefirebegan.Fore】

　　新概念英语第53课HotSnake.Abirdhadsnatchedupthesnakefromtheground.为什么要用过去完成

　　全文内容

　　AtlastfiremenhaveputoutabigforestfireinCalifornia.Sincethen,theyhavebeentryingtofindouthowthefirebegan.Forestfiresareoftencausedbybrokenglassorbycigaretteendswhichpeoplecarelesslythrowaway.Yesterdaythefiremenexaminedthegroundcarefully,butwerenotabletofindanybrokenglass.Theywerealsoquitesurethatacigaretteenddidnotstartthefire.Thismorning,however,afiremenaccidentallydiscoveredthecause.Henoticedtheremainsofasnakewhichwaswoundroundtheelectricwiresofa16,000-voltpowerline.Inthisway,hewasabletosolvethemystery.Theexplanationwassimplebutveryunusual.Abirdhadsnatchedupthesnakefromthegroundandthendroppeditontothewires.Thesnakethenwounditselfroundthewires.Whenitdidso,itsentsparksdowntothegroundandtheseimmediatelystartedafire.