ThehugeFloridawetlandknownastheEvergladesisaslow-movingriver80kilometreswidebutonlyafewcentimetersdeep.PeoplecalltheEvergladesa“riverofgrass”becausesawgrasscoversmostofit.Sawgrassisnotreallygrass.I

　　ThehugeFloridawetlandknownastheEvergladesisaslow-movingriver80kilometreswidebutonlyafewcentimetersdeep.PeoplecalltheEvergladesa“riverofgrass”becausesawgrasscoversmostofit.Sawgrassisnotreallygrass.Itisaplantthathasleavesedgedwithtinysharpteeththatcaneasilycutthroughclothes—andskin!

　　TravelintheEvergladesisdifficult.Youcannotwalkthroughshallowwaterbecausethesawgrasswillcutyou.Thewateristooshallowforregularboats.Soweuseanairboat.Anairboatisaflatopenboat.Likeanairplaneithasabigpropellertomoveit.Thepropellerisfixedontherearoftheboat.Itmakesatremendousnoisebutitdoesthejob.Theboatskimsalongthewater’ssurface.Althoughwecanstillgetlostinanairboatatleastweareabovethealligators(短吻鳄).

　　WhilehundredsofdifferentkindsofanimalsliveintheEvergladesthemostfamousissurelythealligator.OnceendangeredalligatorsarenowprotectedwithinEvergladesNationalPark.Visitorsarelikelytoseethembothonlandandinwater.

　　ForalongtimedangershavethreatenedtheEverglades.Around1900somepeoplefeltthispreciouswetlandshouldbedrained(排干).Theysaiditwasjustabigswampandnotgoodforanything.Inthe1920stherewasalandboominFlorida.PeoplewantedtobuildhomeseverywhereincludingintheEverglades.Theybuiltcanalslevees(防洪堤)andotherwatersystemsthatstoppedtheriversflowingintotheEverglades.Factorieswerebuiltnearriversthatflowedintothewetland.ThesefactoriesdumpedpoisonouswastethatdamagedtheEvergladesecosystem.

　　?PeoplearenowworkingtopreservetheEvergladesNationalParkforthefuture.Rightnowonebigproblemisthepaperbarktree.ThistreeisaninvaderfromAustralia.

　　Paperbarktreessoakupalotofwater.Intheearly1900speoplebroughtthemtoFloridabecausetheythoughttheywouldhelpdraintheEverglades.Howevertheinvadersadaptedtoowell.PaperbarktreeshavetakenoverhundredsofthousandsofacresoftheEvergladesandkilledothertrees.Scientistsarecuttingdowntheseinvadersorsprayingthemwithherbicides(除草剂)tokillthem.?

　　【小题1】WhichhelpstoexplainwhyitisdifficulttotravelinEverglades?

　　A．Airboatsmaymakeaverybignoise.