大连海事大学《考研英语》unitsevenlisteningscript

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1、UnitSevenEnvironmentProtectionPartOneWarm・upListeningPoplarTreesasPollutionFightersPoplartreescanbecutdownandusedforwoodandpape匚Ortheycanbelefttostandandusedfordifferentpurposes・Poplartreesareoftenusedtoguardagainstwaterpollution.Theyareplantedasbarrierstokeepwastefromenteringgroun

2、dwaterandrivers.Theirlargerootsystemstrapwastes,likenitrogen-basedfertilizer,andhelpreducethelossofsoil.Nowpoplartreesmaybecomeimportanttoolsforcleaningtheenvironment.Somescientiststhinkpoplarscanbeavaluableresourcetoremovepoisonoussubstancesfromthesoil.Thepoplartreeisfoundinmanypl

3、acesinthenorthernhalfoftheworld.Itisafastgrowingtreethatrequiresalotofwater.DifferentkindsofpoplartreesarenativetoAsia,EuropeandNorthAmerica.IntheUnitedStates,poplarsarealsoknownascottonwoodtrees.Foryears,professorRichardMeagheroftheUniversityofGeorgiahasdoneresearchongeneticallyen

4、gineeredplants.Heisnowtestingapoplartreethathasbeengeneticallyengineeredtotakeinmercurythroughitsroots・Thetreethenslowlyreleasesthemercuryintotheairthroughitsleaves.Mercuryisahighlypoisonousmetal.Itisawasteproductofmanyindustries.Mercurybuildsupinfishandotherlivingthings.Itisespeci

5、allydangeroustothedevelopmentofchildren・Thisiswhywomenwhomightgetpregnantarewarnedtobecarefulaboutmercurylevelsinthefoodtheyea匚ProfessorMeagheristestinghisgeneticallyengineeredpoplarsonsomelandinDanforth,Connecticut.Thegroundispollutedwithmercuryfromafactoryoncethere.Thescientistha

6、splanted160poplarstoremovethepollution.Noteveryonelikestheideatousethegeneticallyengineeredtreestocollectmercury.Criticssaythiscouldreproducewithwildtreesordisplacethem・Anothercriticismisthatthepoplaronlyspreadmercuryratherthanremoveitfromtheenvironment.Theprofessorsaiditisbetterto

7、spreadmercurythanhaveitallinoneplacewhereitcouldbemoreofahealthrisk・Still,thereisgreatinterestinusingplantstoprocessandcontrolharmfulsubstances.Andpoplartreesareamongthemoststudied.Butusingpoplarsasanaturalbarrieragainstwaterpollutionisnotanewidea・TheChinesehaveusedthemthiswayforth

8、ousandsofyears・(Words：395)