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成就动机理论的主要代表人物阿特金森认为避免失败者的目的是避免失败，减少失败感，所以他们倾向于选择非常容易或非常困难的任务。当一项任务的成功率为50%时，他们会______。
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成就动机理论的主要代表人物阿特金森认为避免失败者的目的是避免失败减少败感当一项任务的成功率为50%时
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成就动机理论的主要代表人物阿特金森认为避免失败者的目的是避免失败减少失败感所以他们倾向于选择非常容易
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Myparentsliveinasmallvillage.Theyalwayskeepcandlesinthehousethereisapowercut.
英语的基本语调有______升调和______
—DidAlanenjoyseeinghisoldfriendsyesterday—Yeshedid.Hehisoldfriendsforalongtime.
InOctober1961atCrowleyFieldinCincinnatiOhioanolddeafgentlemannamedWilliamE.HoystooduptothrowthefirstballoftheWorldSeries.MostpeopleatCrowleyFieldonthatdayprobablydidnotrememberHoybecausehehadretiredfromprofessionalbaseball58yearsearlierin1903.Howeverhehadbeenanoutstandingplayerandthedeafpeoplestilltalkabouthimandhisyearsinbaseball. WilliamE.HoywasborninHouckstownOhioonMay231862.Hebecamedeafwhenhewastwoyearsold.HeattendedtheColumbusOhioSchoolforthedeaf.Aftergraduationhestartedplayingbaseballwhileworkingasashoemaker. Hoybeganplayingprofessionalbaseballin1886forOshkoshWisconsinoftheNorthwesternLeague.In1888hestartedasanoutfielderwiththeoldWashingtonSenators.Hissmallfigureandspeedmadehimanoutstandingbaserunner.Hewasverygoodatstealingbasesduringhiscareer.Inthe1888majorleagueseasonhestole82bases.HewasalsotheSenators’leadinghitterin1888.Hoywascleverandhethrewright-handedandbattedleft-handed.OnJune191889hethrewoutthreebattersattheplatefromhisoutfieldposition. ThearmsignalsusedbyjudgestodaytoshowballsandstrikesbeganbecauseofHoy.Thejudgeliftedhisrightarmtoshowthatthepitchwasastrikeandhisleftarmtosignalthatitwasaball. FormanyyearspeopletalkedaboutHoy’slastballgamein1903.HewasplayingforLosAngelesofthePacificCoastWinterLeague.ItwasamemorablegamebecauseHoyhitawonderfulballwhichwonthegame.Itwasaveryfoggydayandthereforeveryhardtoseetheball.IntheninthinningwithtwomenoutHoymanagedtocatchaflyballtomakethethirdoutinspiteofthefog.LosAngelesdefeatedtheiroppositionandwonthegame. AfterheretiredHoystayedbusy.HeranadairyfarmnearCincinnatifor20years.Healsobecameapublicspeakerandtraveledgivingspeeches.Untilafewyearsbeforehisdeathhetook4～10milewalksseveralmorningsaweek.OnDecember151961WilliamHoydiedattheageof99. Whatcanbeinferredfromthispassage
小学英语课程资源
请结合自己的教学实际论述在教学实践中如何有效使用小学英语教材
Believeitornotopticalillusioncancuthighwaycrashes. Japanisacaseinpoint.Ithasreducedautomobilecrashesonsomeroadsbynearly75percentusingasimpleopticalillusion.Butstripescalledchevronspaintedontheroadsmakedriversthinkthattheyaredrivingfasterthantheyreallyareandthusdriversslowdown. NowtheAmericanAutomobileAssociationFoundationforTrafficSafetyinWashingtonD.C.isplanningtorepeatJapan’ssuccess.Startingnextyearthefoundationwillpaintchevronsandotherpatternsofstripesonselectedroadsaroundthecountrytotesthowwellthepatternsreducehighwaycrashes. Excessivetoogreatspeedplaysamajorroleinasmuchasonefifthofallfataltrafficaccidentsaccordingtothefoundation.Tohelpreducethoseaccidentsthefoundationwillconductitstestsinareaswherespeed-relatedhazardsdangerarethegreatestcurvesexitslopestrafficcirclesandbridges. Somestudiessuggestthatstraighthorizontalbarspaintedacrossroadscaninitiallycuttheaveragespeedofdriversinhalf.Howevertrafficoftenreturnstofullspeedwithinmonthsasdriversbecomeusedtoseeingthepaintedbars. Chevronsscientistssaynotonlygivedriverstheimpressionthattheyaredrivingfasterthantheyreallyarebutalsomakealaneappeartobenarrower.Theresultisalongerlastingreductioninhighwayspeedandthenumberoftrafficaccidents. TheAmericanAutomobileAssociationFoundationforTrafficSafetyplansto
Theboywasseenintheexaminationandwaspunishedbytheteacher.
Iwasasingleparentoffoursmallchildrenworkingatalowpaidjob.Moneywasalwaystightbutwehada1overourheadsfoodonthetableclothesonourbacksandifnotalotalways2.NotknowingwewerepoormykidsjustthoughtIwas3.I’vealwaysbeengladaboutthat. ItwasChristmastimeandalthoughtherewasn’t4foralotofgiftsweplannedtocelebratewithafamilyparty.Butthebig5forthekidswasthefunofChristmas6. Theyplannedweeksaheadoftimeasking7whattheywantedforChristmas.FortunatelyIhadsavedMYM120for8tosharebyallfiveofus. Thebig9arrived.Igaveeachkidatwenty-dollarbilland10themtolookforgiftsofaboutfourdollarseach.Theneveryonescattered.Wehadtwohourstoshop;thenwewould11backatthe"Santa’sWorkshop". DrivinghomeeveryonewasinhighChristmasspirits12myyoungerdaughterGingerwhowasunusually13.Shehadonlyonesmallflatbagwithafewcandies—fiftycentcandies!IwassoangrybutIdidn’tsayanything14wegothome.Icalledherintomybedroomandclosedthedoor15tobeangryagain.Thisiswhatshetoldme. "Iwaslooking16thinkingofwhattobuyandI17toreadthelittlecardsonthe’GivingTrees’.Onewasforalittlegirlfouryearsoldandallshe18forChristmaswasadoll.SoItookthecardoffthetreeand19thedollforher.Wehavesomuchandshedoesn’thaveanything." Ineverfeltso20asIdidthatday. 6
Somespidershuntonthegroundothersbuildwebstotraptheirfoodbutthegrasswaterspidercatchesitspreybyrunningalongthesurfaceofthewater. Thisspecialwaterspiderlivesonthegrassybanksofstreamswheremosquitoesdamselfliesandotherinsectscometofeedandbreed. AlthoughitisoneofthelargestspidersinNewZealandithasanunusualability.Itdoesn’tdisturbthewaterasitwaitsforitsmealandthereisbarelyaripplewhenitskimsacrossthesurfaceatlightningspeedtocatchitsprey. Grasswaterspidersdealswiftlywithlargerinsectslikedamselfliesbypullingtheirheadsunderthewaterandholdingthemthereuntiltheydrown. Afteramealthegrasswaterspiderspendsuptohalfanhourgroomingitself.Itwipesitseighteyesbrushesitsantennaeandtakesspecialcaretocleanthehairsonitsbody. Itisthehairsthattraptinybubblesofairsothatthespidercanrundownabladeofgrassandstayunderwaterforuptoanhourwhenitisfrightened.Thehairsalsokeepthespiderdryevenunderwater. Itisonlywhenthefemalespideriscaringfortheyoungthatshedoesnothuntonthewater.Aftermatingsheproducesalargeeggsacwhichshecarriesaroundforfiveweeks.Oncetheeggsstarttohatchsheattachesthesactosomebladesofgrassorathistle.Shethentearsthesacopenandreleasesthetinyspidersintothenurseryweb. Thewriterdescribesthespecialspiderasspecialbecause
Iwasasingleparentoffoursmallchildrenworkingatalowpaidjob.Moneywasalwaystightbutwehada1overourheadsfoodonthetableclothesonourbacksandifnotalotalways2.NotknowingwewerepoormykidsjustthoughtIwas3.I’vealwaysbeengladaboutthat. ItwasChristmastimeandalthoughtherewasn’t4foralotofgiftsweplannedtocelebratewithafamilyparty.Butthebig5forthekidswasthefunofChristmas6. Theyplannedweeksaheadoftimeasking7whattheywantedforChristmas.FortunatelyIhadsavedMYM120for8tosharebyallfiveofus. Thebig9arrived.Igaveeachkidatwenty-dollarbilland10themtolookforgiftsofaboutfourdollarseach.Theneveryonescattered.Wehadtwohourstoshop;thenwewould11backatthe"Santa’sWorkshop". DrivinghomeeveryonewasinhighChristmasspirits12myyoungerdaughterGingerwhowasunusually13.Shehadonlyonesmallflatbagwithafewcandies—fiftycentcandies!IwassoangrybutIdidn’tsayanything14wegothome.Icalledherintomybedroomandclosedthedoor15tobeangryagain.Thisiswhatshetoldme. "Iwaslooking16thinkingofwhattobuyandI17toreadthelittlecardsonthe’GivingTrees’.Onewasforalittlegirlfouryearsoldandallshe18forChristmaswasadoll.SoItookthecardoffthetreeand19thedollforher.Wehavesomuchandshedoesn’thaveanything." Ineverfeltso20asIdidthatday. 4
Heisonlytooreadytohelpothersseldomrefusingthemwhentheyturntohim.
稍等一会儿我会帮助你的
AcharacteristicofAmericanculturethathasbecomealmostatraditionistorespecttheself-mademan—themanwhohasrisentothetopthroughhisowneffortsusuallybeginningbyworkingwithhishands.WhiletheleaderinbusinessorindustryorthecollegeprofessoroccupiesahighersocialpositionandcommandsgreaterrespectinthecommunitythanthecommonlaboreroreventheskilledfactoryworkerhemaytakepainstopointoutthathisfatherstartedlifeinAmericaasafarmerorlaborerofsomesort. ThisattitudetowardmanuallaborisnowstillseeninmanyaspectsofAmericanlife.Oneisinvitedtodinneratahomethatisnotonlycomfortablybutevenluxuriouslyfurnishedandinwhichthereiseveryevidenceofthefactthatthefamilyhasbeenabletoaffordforeigntravelexpensivehobbiesandcollegeeducationforthechildren;yetthehostessprobablywillcookthedinnerherselfwillserveitherselfandwillwashdishesafterwardfurthermorethedinnerwillnotconsistmerelyofsomethingquicklyandeasilyassembledfromcontentsofvariouscansandacakeorapieboughtatthenearbybakery.Onthecontrarythehostessusuallytakesprideincarefulpreparationofspecialdishes.Aprofessionalmanmaytalkaboutwashingthecardigginginhisflowerbedspaintingthehouse.Hiswifemayevenhelpwiththesethingsjustasheoftenhelpsherwiththedishwashing.Thesonwhoisawayatcollegemaywaitontableandwashdishesforhislivingorduringthesummerhemayworkwithaconstructiongangonahighwayinordertopayforhiseducation. Fromparagraph1wecanknowthatinAmerica
不仅我而且汤姆和玛丽都喜欢游泳
Believeitornotopticalillusioncancuthighwaycrashes. Japanisacaseinpoint.Ithasreducedautomobilecrashesonsomeroadsbynearly75percentusingasimpleopticalillusion.Butstripescalledchevronspaintedontheroadsmakedriversthinkthattheyaredrivingfasterthantheyreallyareandthusdriversslowdown. NowtheAmericanAutomobileAssociationFoundationforTrafficSafetyinWashingtonD.C.isplanningtorepeatJapan’ssuccess.Startingnextyearthefoundationwillpaintchevronsandotherpatternsofstripesonselectedroadsaroundthecountrytotesthowwellthepatternsreducehighwaycrashes. Excessivetoogreatspeedplaysamajorroleinasmuchasonefifthofallfataltrafficaccidentsaccordingtothefoundation.Tohelpreducethoseaccidentsthefoundationwillconductitstestsinareaswherespeed-relatedhazardsdangerarethegreatestcurvesexitslopestrafficcirclesandbridges. Somestudiessuggestthatstraighthorizontalbarspaintedacrossroadscaninitiallycuttheaveragespeedofdriversinhalf.Howevertrafficoftenreturnstofullspeedwithinmonthsasdriversbecomeusedtoseeingthepaintedbars. Chevronsscientistssaynotonlygivedriverstheimpressionthattheyaredrivingfasterthantheyreallyarebutalsomakealaneappeartobenarrower.Theresultisalongerlastingreductioninhighwayspeedandthenumberoftrafficaccidents. Onroadspaintedwithchevronsdriverstendtofeelthat
请脱下你的旧上衣穿上这件新的
Theaveragepersonlearnsmostofthe30000～40000wordswhosemeaningsheorsherecognizesbyhearingthemorgettingfamiliarwiththeminthecontextorsimplyabsorbingthemwithoutconsciouseffort.Thebestwaytobuildagoodvocabularythereforeistoreadagreatdealandtoparticipateinalotofgoodtalks.Therearerelativelyfewwordsthatwelearnpermanentlybypurposefullyreferringtodictionariesorkeepingwordlists.Howevereventhoseextrafewareofvalueandnoonewillmakeamistakebyworkingondevelopingalargervocabulary.Herearesomesuggestionsofhowtodoit. Readplentyofgoodbooks.Whenyoucomeacrossanewwordoranewmeaningofanoldwordstopandseeifyoucanunderstanditfromitscontext.Ifyoucan’tandifyoucanmanagewithoutinterruptingthethoughtofthebooktoomuchlookitupinadictionaryorasksomebodyandthenrepeatitsmeaningtoyourselfacoupleoftimes.Ifyouarereallyconscientiouswritethewordanditsmeaninginapersonalvocabularylist—preferablyusingitinasentenceoryoucankeepaspecialvocabularynotebook.Gooverthelistfromtimetotime.Furthertrytouseanewwordinwritingorconversationafewtimesoverthenextseveraldays. Listentogoodtalksandbealerttonewwordsyouhearortonewmeaningsofwordsyoualreadyknow.Thentreatthemjustasyoutreatthenewwordsyouread. Learnandbealerttothepartsofwords:prefixessuffixesandroots.Knowingthemenablesyoutomakeintelligentguessesaboutthemeaningofwords. IfyouarestudyingaforeignlanguagebealerttowordsinthatlanguagewhichrelatetowordsinEnglish.Englishhasinheritedorborrowedmuchofitsvocabularyof500000～600000wordsfromLatinGreekFrenchSpanishandGerman. Whenyoumeetanewwordinreadingwhatshouldyoudo
Wehopetogotothebeachtomorrowbutwewon'tgoit'sraining.
Somespidershuntonthegroundothersbuildwebstotraptheirfoodbutthegrasswaterspidercatchesitspreybyrunningalongthesurfaceofthewater. Thisspecialwaterspiderlivesonthegrassybanksofstreamswheremosquitoesdamselfliesandotherinsectscometofeedandbreed. AlthoughitisoneofthelargestspidersinNewZealandithasanunusualability.Itdoesn’tdisturbthewaterasitwaitsforitsmealandthereisbarelyaripplewhenitskimsacrossthesurfaceatlightningspeedtocatchitsprey. Grasswaterspidersdealswiftlywithlargerinsectslikedamselfliesbypullingtheirheadsunderthewaterandholdingthemthereuntiltheydrown. Afteramealthegrasswaterspiderspendsuptohalfanhourgroomingitself.Itwipesitseighteyesbrushesitsantennaeandtakesspecialcaretocleanthehairsonitsbody. Itisthehairsthattraptinybubblesofairsothatthespidercanrundownabladeofgrassandstayunderwaterforuptoanhourwhenitisfrightened.Thehairsalsokeepthespiderdryevenunderwater. Itisonlywhenthefemalespideriscaringfortheyoungthatshedoesnothuntonthewater.Aftermatingsheproducesalargeeggsacwhichshecarriesaroundforfiveweeks.Oncetheeggsstarttohatchsheattachesthesactosomebladesofgrassorathistle.Shethentearsthesacopenandreleasesthetinyspidersintothenurseryweb. Thepurposeofthepassageisto
Theaveragepersonlearnsmostofthe30000～40000wordswhosemeaningsheorsherecognizesbyhearingthemorgettingfamiliarwiththeminthecontextorsimplyabsorbingthemwithoutconsciouseffort.Thebestwaytobuildagoodvocabularythereforeistoreadagreatdealandtoparticipateinalotofgoodtalks.Therearerelativelyfewwordsthatwelearnpermanentlybypurposefullyreferringtodictionariesorkeepingwordlists.Howevereventhoseextrafewareofvalueandnoonewillmakeamistakebyworkingondevelopingalargervocabulary.Herearesomesuggestionsofhowtodoit. Readplentyofgoodbooks.Whenyoucomeacrossanewwordoranewmeaningofanoldwordstopandseeifyoucanunderstanditfromitscontext.Ifyoucan’tandifyoucanmanagewithoutinterruptingthethoughtofthebooktoomuchlookitupinadictionaryorasksomebodyandthenrepeatitsmeaningtoyourselfacoupleoftimes.Ifyouarereallyconscientiouswritethewordanditsmeaninginapersonalvocabularylist—preferablyusingitinasentenceoryoucankeepaspecialvocabularynotebook.Gooverthelistfromtimetotime.Furthertrytouseanewwordinwritingorconversationafewtimesoverthenextseveraldays. Listentogoodtalksandbealerttonewwordsyouhearortonewmeaningsofwordsyoualreadyknow.Thentreatthemjustasyoutreatthenewwordsyouread. Learnandbealerttothepartsofwords:prefixessuffixesandroots.Knowingthemenablesyoutomakeintelligentguessesaboutthemeaningofwords. IfyouarestudyingaforeignlanguagebealerttowordsinthatlanguagewhichrelatetowordsinEnglish.Englishhasinheritedorborrowedmuchofitsvocabularyof500000～600000wordsfromLatinGreekFrenchSpanishandGerman. Thephrasebealerttointhethirdparagraphmaybestbereplacedby.
AcharacteristicofAmericanculturethathasbecomealmostatraditionistorespecttheself-mademan—themanwhohasrisentothetopthroughhisowneffortsusuallybeginningbyworkingwithhishands.WhiletheleaderinbusinessorindustryorthecollegeprofessoroccupiesahighersocialpositionandcommandsgreaterrespectinthecommunitythanthecommonlaboreroreventheskilledfactoryworkerhemaytakepainstopointoutthathisfatherstartedlifeinAmericaasafarmerorlaborerofsomesort. ThisattitudetowardmanuallaborisnowstillseeninmanyaspectsofAmericanlife.Oneisinvitedtodinneratahomethatisnotonlycomfortablybutevenluxuriouslyfurnishedandinwhichthereiseveryevidenceofthefactthatthefamilyhasbeenabletoaffordforeigntravelexpensivehobbiesandcollegeeducationforthechildren;yetthehostessprobablywillcookthedinnerherselfwillserveitherselfandwillwashdishesafterwardfurthermorethedinnerwillnotconsistmerelyofsomethingquicklyandeasilyassembledfromcontentsofvariouscansandacakeorapieboughtatthenearbybakery.Onthecontrarythehostessusuallytakesprideincarefulpreparationofspecialdishes.Aprofessionalmanmaytalkaboutwashingthecardigginginhisflowerbedspaintingthehouse.Hiswifemayevenhelpwiththesethingsjustasheoftenhelpsherwiththedishwashing.Thesonwhoisawayatcollegemaywaitontableandwashdishesforhislivingorduringthesummerhemayworkwithaconstructiongangonahighwayinordertopayforhiseducation. Theexpressionwaitontableinthesecondparagraphmeans.
Georgecouldn'trememberwhenhefirstmetMr.AndersonbuthewassureitwasSundaybecauseeverybodywasatchurch.
InOctober1961atCrowleyFieldinCincinnatiOhioanolddeafgentlemannamedWilliamE.HoystooduptothrowthefirstballoftheWorldSeries.MostpeopleatCrowleyFieldonthatdayprobablydidnotrememberHoybecausehehadretiredfromprofessionalbaseball58yearsearlierin1903.Howeverhehadbeenanoutstandingplayerandthedeafpeoplestilltalkabouthimandhisyearsinbaseball. WilliamE.HoywasborninHouckstownOhioonMay231862.Hebecamedeafwhenhewastwoyearsold.HeattendedtheColumbusOhioSchoolforthedeaf.Aftergraduationhestartedplayingbaseballwhileworkingasashoemaker. Hoybeganplayingprofessionalbaseballin1886forOshkoshWisconsinoftheNorthwesternLeague.In1888hestartedasanoutfielderwiththeoldWashingtonSenators.Hissmallfigureandspeedmadehimanoutstandingbaserunner.Hewasverygoodatstealingbasesduringhiscareer.Inthe1888majorleagueseasonhestole82bases.HewasalsotheSenators’leadinghitterin1888.Hoywascleverandhethrewright-handedandbattedleft-handed.OnJune191889hethrewoutthreebattersattheplatefromhisoutfieldposition. ThearmsignalsusedbyjudgestodaytoshowballsandstrikesbeganbecauseofHoy.Thejudgeliftedhisrightarmtoshowthatthepitchwasastrikeandhisleftarmtosignalthatitwasaball. FormanyyearspeopletalkedaboutHoy’slastballgamein1903.HewasplayingforLosAngelesofthePacificCoastWinterLeague.ItwasamemorablegamebecauseHoyhitawonderfulballwhichwonthegame.Itwasaveryfoggydayandthereforeveryhardtoseetheball.IntheninthinningwithtwomenoutHoymanagedtocatchaflyballtomakethethirdoutinspiteofthefog.LosAngelesdefeatedtheiroppositionandwonthegame. AfterheretiredHoystayedbusy.HeranadairyfarmnearCincinnatifor20years.Healsobecameapublicspeakerandtraveledgivingspeeches.Untilafewyearsbeforehisdeathhetook4～10milewalksseveralmorningsaweek.OnDecember151961WilliamHoydiedattheageof99. WecaninferfromthelastparagraphthatHoyinhislateyears.
Theseasideheredrawsalotoftouristseverysummer.Warmsunshineandsoftsandsmakeitis.
Iwasasingleparentoffoursmallchildrenworkingatalowpaidjob.Moneywasalwaystightbutwehada1overourheadsfoodonthetableclothesonourbacksandifnotalotalways2.NotknowingwewerepoormykidsjustthoughtIwas3.I’vealwaysbeengladaboutthat. ItwasChristmastimeandalthoughtherewasn’t4foralotofgiftsweplannedtocelebratewithafamilyparty.Butthebig5forthekidswasthefunofChristmas6. Theyplannedweeksaheadoftimeasking7whattheywantedforChristmas.FortunatelyIhadsavedMYM120for8tosharebyallfiveofus. Thebig9arrived.Igaveeachkidatwenty-dollarbilland10themtolookforgiftsofaboutfourdollarseach.Theneveryonescattered.Wehadtwohourstoshop;thenwewould11backatthe"Santa’sWorkshop". DrivinghomeeveryonewasinhighChristmasspirits12myyoungerdaughterGingerwhowasunusually13.Shehadonlyonesmallflatbagwithafewcandies—fiftycentcandies!IwassoangrybutIdidn’tsayanything14wegothome.Icalledherintomybedroomandclosedthedoor15tobeangryagain.Thisiswhatshetoldme. "Iwaslooking16thinkingofwhattobuyandI17toreadthelittlecardsonthe’GivingTrees’.Onewasforalittlegirlfouryearsoldandallshe18forChristmaswasadoll.SoItookthecardoffthetreeand19thedollforher.Wehavesomuchandshedoesn’thaveanything." Ineverfeltso20asIdidthatday. 2
教学目标包括情感目标知识目标和______
Itisclearthatsomechemicalscandamagethehealthofanimalsandhumans.1thisisnottheonlyproblemthat2becausedbythecarelessuseofchemicals.Chemicalscanalso3theecologicalbalanceoftheenvironment.Iftheecologicalbalanceisdisturbedtheresultscanbe4serious. The5ofDDTillustratestheproblem.DDTachemicalwhichkillsinsectsatfirstseemedtobeaperfectanswer6manyproblems.Itwouldcontrolinsectsthatcauseddangerousdiseases7insectsthatcausedbillionsofdollarsofdamagetocropseveryyear.Governmentspermittedandeven8theuseofDDT.Farmersinmanycountries9tosprayitontheircrops.The10resultsweregood:Damagetocrops11downandprofitswentup.Howeverthechemicalhadeffectswhichthescientistsdidn’tseein12.Firstitalsokilledinsectswhichwerethe13enemiesoftheharmfulinsectsandwhichwerethereforebeneficialtofarmers.SecondandperhapsworseDDTdidnotkill14harmfulinsect.Afewinsectshadnaturalresistancetothechemical.They15andreproducedinlargenumbers.Inafewyearstherewerelargenumbersofinsectswhichwerenot16byDDTandtherewere17insectswhichcouldactasnatural18onthesenew"super-insects".FinallyitbecameclearthatDDTwasnotsolvingtheinsectproblem.Infactitwasmakingtheproblemworse.It19becamenecessarytofindasecond20fortheeffectsofthefirst. 18
Itisclearthatsomechemicalscandamagethehealthofanimalsandhumans.1thisisnottheonlyproblemthat2becausedbythecarelessuseofchemicals.Chemicalscanalso3theecologicalbalanceoftheenvironment.Iftheecologicalbalanceisdisturbedtheresultscanbe4serious. The5ofDDTillustratestheproblem.DDTachemicalwhichkillsinsectsatfirstseemedtobeaperfectanswer6manyproblems.Itwouldcontrolinsectsthatcauseddangerousdiseases7insectsthatcausedbillionsofdollarsofdamagetocropseveryyear.Governmentspermittedandeven8theuseofDDT.Farmersinmanycountries9tosprayitontheircrops.The10resultsweregood:Damagetocrops11downandprofitswentup.Howeverthechemicalhadeffectswhichthescientistsdidn’tseein12.Firstitalsokilledinsectswhichwerethe13enemiesoftheharmfulinsectsandwhichwerethereforebeneficialtofarmers.SecondandperhapsworseDDTdidnotkill14harmfulinsect.Afewinsectshadnaturalresistancetothechemical.They15andreproducedinlargenumbers.Inafewyearstherewerelargenumbersofinsectswhichwerenot16byDDTandtherewere17insectswhichcouldactasnatural18onthesenew"super-insects".FinallyitbecameclearthatDDTwasnotsolvingtheinsectproblem.Infactitwasmakingtheproblemworse.It19becamenecessarytofindasecond20fortheeffectsofthefirst. 20
认知法的理论基础为______和______
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