学术综合英语听力原文完整版Word下载.doc

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RoadBuilding

Goodmorning,everyone.TodayI'

llbetalkingabouttherelationshipbetweenroadbuildingandthedevelopmentoftheAmericaneconomyduringthe18thcentury.About300yearsago,theUnitedStates'

economywasgrowingrapidly,mainlybecauseofaboomingtradeintwoimportantagriculturalproducts:

grainandcotton.

GrainoutputintheeasternpartofAmericaincreasedquicklyatthattimeduetotherapidlygrowingpopulationandthelargenumberofimmigrantsfromEurope.Asaresult,thedemandforgrainalmostdoubled.Forthisreason,thetradeingrainfirstdevelopedinthispartofthecountry.Atthesametime,theroadsystemwasgraduallybuiltupinordertotransportthegrainfromtheruralareastovariouscities.Theroadbuildingclearlyhelpeddeveloptheeconomyquicklyintheseareasandinthecitiesaswell.

Duringthesameperiod,farmersintheSouthcouldgetalargeamountoflaborersfromAfrica,andtheystartedtogrowcotton.Asthecottonoutputincreased,thefarmersneededtosellitinotherplaces.Asaresult,manyroadswerebuilttolinktheruralareastothecities.

Atfirst,thistradeofgrainandcottontookplacealongthecoast,ornearriversandlakes.Ittookplacetherebecauseitwaseasyandcheaptotransportgoodsfromoneplacetoanother.Before1700,itwasveryexpensivetomovethegoodsbyroad.So,farmershadtorelymainlyonriverstomovetheircropstomarkets.

Atthattime,therewasonlyonecontinuousroadthatexistedintheUS.Itranfromnorthtosouthalongcountryroads,whichwerelinkedtogethertomakeonelongroad.Withinashorttime,thefirsteast-to-westroadswerebuilt.Theywerecalledturnpikes.Privatecompaniesbuilttheseroadsandcollectedfeesfromallvehiclesthattraveledonthem.

Eventually,becauseoftheboomingtradeofgrainandcotton,anetworkofroadwayswascompletedthatconnectedsomemajorcitiesandtowns.Althoughtravelingwasstillcostlyforfarmers,theysoonpreferredtomovetheircropstocitiesandotherareasonroadwaysratherthanbyboatbecauseitwasfasterandmoreconvenient.

SoherewecanseearatherclearpictureofroadbuildingintheUnitedStatesanditsimpactoneconomicdevelopmentduringthatperiod.

TheMississippiRiverinAmerica

Goodafternoon.Todaywe’regoingtotalkabouttheMississippiRiver.TheMississippiRiveristhelargestriveroftheNorthAmerica.Itsmajortributariesdrainanareaofapproximately3,000,000squarekilometers,oraboutone-eighthoftheentirecontinent.TheMississippiRiverliesentirelyintheUnitedStates.FromitssourceatLakeItascainMinnesota,itflowsfromtheNorthalmostduesouthacrossthecontinentalinterior,collectingthewatersofitsmajortributaries,downtotheGulfofMexico.TheMightyMississippi,asitisaffectionatelyknown,flowsatotaldistanceabout4,000kilometersfromitssource.Withitstributaries,theMississippidrainsallorpartof31U.S.statesandtwoCanadianprovinces.

Aseveryoneknows,inthepasttheriverwasthemostimportantwayoftransportinggoodsfromtheNorthtotheSouth,orfromtheSouthtotheNorthintheUnitedStates.

TheMississippiRiverisalsoariverthatcansometimesgetoutofcontrolandcauseseriousfloodinginsummer.Nowadaysengineersusefourdifferentmethodstocontrolthefloodwatersoftheriver.Thesefourwaysare:

floodways,dams,leveesandreservoirs.I'

lldiscusseachofthesehere.

FloodwaysarethefirstwayofcontrollingthefloodwatersoftheMississippiRiver.Floodwaysareemptychannelsreadytoholdwaterfromtheriver.WhentheMississippiRiveristoohigh,thefloodwaysareopenedandsomeofthewatercanflowintothefloodways.ThereareseveralfloodwaysalongthelowerMississippiRiver,whichhelppreventfloodingeffectively.

ThesecondwayofcontrollingthefloodwatersoftheMississippiRiveriswithdams.Damsarewallsthatarebuiltacrossarivertocontrolthewater.Therearemorethan30damsontheMississippiRiver.Damscontrolthewaterbyholdingthewaterbehindthemuntiladecisionismadetoreleaseit.

LeveesareathirdwayofcontrollingthefloodwatersoftheMississippiRiver.Leveesareearthenwallsbuiltalongsideariver.Theyholdthewaterintheriverandkeepitfromcoveringthelandbesidetheriver.Therearemorethan2,000milesofleveesalongtheMississippiRiver.

Inthe19thand20thcenturies,severalreservoirswerebuiltalongtheMississippiRivertoharnessthewater.Theyhavetwofunctions.Oneistoholdwater,andtheotheristogenerateelectricitythroughhydroelectricpowerstations.Sincethe20thcentury,nohugefloodhasbrokenoutoftheMississippiRiver.

Unit2EnergyConservation

AnEyewitnesstoChangesinChina

（Y:

YangRui,anchorofDialogue,CCTV-9