2009年6月英语四级考试模拟样题及解答

PartⅠWriting(30minutes)Directions:Forthispart,youareallowed30minutestowriteashortessayentitledTheDecreaseofPublicTransportationTicketFare.Youshouldwriteatleast120wordsfollowingtheoutlinegivenbelow:1.近来一些城市政府实施多项举措降低公共交通票价，大力发展公共交通;2.此措施带来的好处;3.作为市民应如何响应政府的号召。TheDecreaseofPublicTransportationTicketFarePartⅡReadingComprehension(SkimmingandScanning)(15minutes)Directions:Inthispart,youwillhave15minutestogooverthepassagequicklyandanswerthequestionsonAnswerSheet1.Forquestions1-7,choosethebestanswerfromthefourchoicesmarkedA),B),C)andD).Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.TheDebateOverGeneticallyModifiedFoodsForthousandsofyearsfarmershaveusedaprocessofselectionandcrossbreedingtocontinuallyimprovethequalityofcrops.Traditionalbreedingmethodsareslow,requiringintensivelabor:whiletryingtogetadesirabletraitinabredspecies,undesirabletraitswillappearandfarmersmustcontinuetheprocessoverandoveragainuntilalltheundesirablesarebredout.Incontrast,organismsacquireonespecificgeneorafewgenestogetherthroughgeneticmodification,withoutothertraitsincludedandwithinasinglegeneration.However,thistechnologytooisinherentlyunpredictableandsomescientistsbelieveitcanproducepotentiallydangerousresultsunlessbettertestingmethodsaredeveloped.Traditionalbreedingisbasedonsexualreproductionbetweenlikeorganisms.Thetransferredgenesaresimilartogenesinthecelltheyjoin.Theyareconveyedincompletegroupsandinafixedsequencethatharmonizeswiththesequenceofgenesinthepartnercell.Incontrast,bioengineersisolateagenefromonetypeoforganismandcollectitrandomlyintotheDNAofadissimilarspecies,disruptingitsnaturalsequence.Oneofthemaindifferencesbetweenconventionalandgeneticallymodifiedcropsisthattheformerinvolvescrosseseitherwithinspeciesorbetweenverycloselyrelatedspecies.However,GMcropscanhavegenesfromcloselyrelatedspeciesorevenfrombacteriaandviruses.Benefits:onesideofthedebateEconomical?GMsupporterstellfarmersthattheystandtoreapenormousprofitsfromgrowingGMcrops.Ittakesashortertimetoproducethedesiredproduct.Itispreciseandtherearenounwantedgenes.ToproducetheGMcrops,modernbiotechnologyisusedwhichrequireshighlyskilledpeopleandsophisticatedandexpensiveequipment.Largecompaniesneedconsiderableinvestmentsinlaboratories,equipmentandhumanresources,hencethereasonwhyGMcropsaremoreexpensiveforfarmersthantraditionalcrops.Herbicide-resistantcropsSowhatotheradvantagesdoGMcropsholdforfarmers?GMcropscanbeproducedtobeherbicide(除草剂)resistant.Thismeansthatfarmerscouldspraythesecropswithherbicideandkilltheweeds,withoutaffectingthecrop.Ineffect,theamountofherbicideusedinoneseasonwouldbereduced,withasubsequentreductionincostsforfarmersandconsumers.Biotechnologycompaniesareevenexperimentingwithcropsthatcanbegeneticallymodifiedtobedroughtandsalt-tolerant,orlessreliantonfertilizer,openingupnewareastobefarmedandleadingtoincreasedproductivity.However,theclaimsoflessherbicideusagewithGMcropshavetillnownotbeenindependentlysupportedbyfacts.BetterqualityfoodsEvenanimalscanbegeneticallymodifiedtobeleaner,growfaster,andneedlessfood.Theycouldbemodifiedtohavespecialcharacteristics,suchasgreatermilkproductionincows.Thesemodificationsagainleadtoimprovedproductivityforfarmersandfinallylowercostsfortheconsumers.Modifiedcropscouldperhapspreventoutbreakssuchasfootandmouthdisease,whichhasbadlyinfluencedmanyfarmersandlocaleconomies.Nosuchproductshavebeenreleasedtodate;however,someareunderconsiderationforrelease.Forexample,GMsalmon,capableofgrowingalmost30timesfasterthannaturalsalmon,maysoonbeapprovedbytheFDA(FoodandDrugAdministration)intheU.S.forreleaseintoopenwaterswithoutasinglestudyontheimpactonhumanhealthortheenvironment.Risks:theothersideofthedebateEnvironmentaldamageTheproblemwithGMcropsisthatthereislittleknownaboutwhateffecttheywillhavein,say,20yearstime.ThegeneticstructureofanylivingorganismiscomplexandGMcroptestsfocusonshort-termeffects.Notalltheeffectsofintroducingaforeigngeneintothecomplexgeneticstructureofanorganismaretested.Willthepeststhatacropwascreatedtoresisteventuallybecomeresistanttothiscrop?ThenthereisalwaysthepossibilitythatwemaynotbeabletodestroyGMcropsoncetheyspreadintotheenvironment.Risktofoodweb.Afurthercomplicationisthatthepesticideproducedinthecropmayunintentionallyharmcreatures.GMcropsmayalsoposeahealthrisktonativeanimalsthateatthem.Theanimalsmaybepoisonedbythebuilt-inpesticides.TestsintheU.S.showedthat44%ofcaterpillars(毛虫)ofthemonarchbutterflydiedwhenfedlargeamountsofpollen(花粉)fromGMcorn.Disease.Anotherconcernisdisease.SincesomecropsaremodifiedusingtheDNAfromvirusesandbacteria,willweseenewdiseasesemerge?WhatabouttheGMcropsthathaveantibiotic-resistantmarkergenes?Markergenesareusedbyscientiststodeterminewhethertheirgeneticmodificationofaplantwassuccessful.Willtheseantibiotic-resistantgenesbetransferredtomicroorganismsthatcausedisease?Wealreadyhaveaproblemwithineffectiveantibiotics.Howcanwedevelopnewdrugstofightthesenewbugs?UntilfurtherstudiescanshowthatGMfoodsandcropsdonotposeseriousthreatstohumanhealthortheworld'secosystems,thedebateovertheirreleasewill