大连海事大学《考研英语》unit7listeningtapescriptandnotes

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1、UnitSevenEnvironmentProtectionPartOneWarm-upListeningPoplarTreesasPollutionFightersTaskOnePoplartreescanbecutdownandusedforwoodandpaper.Ortheycanbelefttostandandusedfordifferentpurposes.Poplartreesareoftenusedtoguardagainstwaterpollution.Theyareplantedasbairierstoke

2、epwastefromenteringgroundwaterandrivers.Theirlargerootsystemstrapwastes,likenitrogen-basedfertilize匚andhelpreducethelossofsoil.Nowpoplartreesmaybecomeimportanttoolsforcleaningtheenvironment.Somescientiststhinkpoplarscanbeavaluableresourcetoremovepoisonoussubstancesf

3、romthesoil.Thepoplartreeisfoundinmanyplacesinthenorthernhalfoftheworld.Itisafastgrowingtreethatrequiresalotofwate匸DifferentkindsofpoplartreesarenativetoAsia,EuropeandNorthAmerica.IntheUnitedStates,poplarsarealsoknownascottonwoodtrees.Foryears,professorRichardMeagher

4、oftheUniversityofGeorgiahasdoneresearchongeneticallyengineeredplants.Heisnowtestingapoplartreethathasbeengeneticallyengineeredtotakeinmercurythroughitsroots.Thetreethenslowlyreleasesthemercuryintotheairthroughitsleaves.Mercuryisahighlypoisonousmetal.Itisawasteproduc

5、tofmanyindustries.Mercurybuildsupinfishandotherlivingthings.Itisespeciallydangeroustothedevelopmentofchildren.Thisiswhywomenwhomightgetpregnantarewarnedtobecarefulaboutmercurylevelsinthefoodtheyeat.ProfessorMeagheristestinghisgeneticallyengineeredpoplarsonsomelandin

6、Danforth,Connecticut.Thegroundispollutedwithmercuryfromafactoryoncethere.Thescientisthasplantedonehundredsixtypoplarstoremovethepollution.Noteveryonelikestheideatousethegeneticallyengineeredtreestocollectmercury.Criticssaythiscouldreproducewithwildtreesordisplacethe

7、m.Anothercriticismisthatthepoplaronlyspreadmercuryratherthanremoveitfromtheenvironment.Theprofessorsaiditisbettertospreadmercurythanhaveitallinoneplacewhereitcouldbemoreofahealthrisk.Still,thereisgreatinterestinusingplantstoprocessandcontrolharmfulsubstances.Andpopl

8、artreesareamongthemoststudied.Butusingpoplarsasanaturalbarrieragainstwaterpollutionisnotanewidea.TheChinesehaveusedthemthiswayforthousands