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1、托福作文写作范文详解ReadingCarmanufacturersandgovernmentshavebeeneagerlyseekingareplacementfortheautomobilesmainsourceofpower,theinternal-combustionengine.Byfarthemostpromisingalternativesourceofenergyforcarsisthehydrogen-basedfuelcellengine,whichuseshydrogentocreateelectricitythat,inturnzpowersthecar.Fuel-ce
2、llengineshaveseveraladvantagesoverinternal-combustionenginesandwillprobablysoonreplacethem.Oneofthemainproblemswiththeinternal-combustionengineisthatitreliesonpetroleum,eitherintheformofgasolineordieselfuel.Petroleumisafiniteresource;someday,wewillrunoutofoil.Thehydrogenneededforfuel-cellenginescann
3、oteasilybedepleted.Hydrogencanbederivedfromvariousplentifulsources,includingnaturalgasandevenwater.Thefactthatfuel-cellenginesutilizeeasilyavailable,renewableresourcesmakesthemparticularlyattractive.Secondzhydrogen-basedfuelcellsareattractivebecausetheywillsolvemanyoftheworldspollutionproblems.Anuna
4、voidableby-productofburningoiliscarbondioxidezandcarbondioxideharmstheenvironmentOntheotherhand,theonlybyproductoffuel-cellenginesiswater.Third,fuel-cellengineswillsoonbeeconomicallycompetitivebecausepeoplewillspendlessmoneytooperateafuel-cellenginethantheywilltooperateaninternal-combustionengine.Th
5、isistrueforonesimplereason:afuel-cellautomobileisnearlytwiceasefficientinusingitsfuelasanautomobilepoweredbyaninternal-combustionengineis.Inotherwords,thefuel-cellpoweredcarrequiresonlyhalfthefuelenergythattheinternalcombustionpoweredcardoestogothesamedistance.ListeningProfessor:Thereadingiscorrecti
6、npointingouttheproblemsassociatedwithoil-poweredcars.Yeszoilisafiniteresource,andyes,burningoilharmstheenvironment.Howeverzthereadingiswaytoooptimisticinitsassessmentofhydrogen-basedfuel-cellengines.Hydrogenisnotthesolutiontotheseproblems.Firstzhydrogenisnotaseasilyavailableasthepassageindicates.Alt
7、houghitspresentincommonsubstanceslikewater,itsnotdirectlyuseableinthatform.Forusingafuel-cellengine,hydrogenmustfirstbeobtainedinapureliquidstate.Thispureliquidhydrogenisahighlyartificialsubstance.Itstechnologicallyverydifficulttoproduceandstoreliquidhydrogen.Forexample,itmustbekeptveryverycoldatmin
8、us253degreesCelsius.Imaginetheelaboratecoolingtechnologythatsrequiredforthat!Sohydrogenisnotsuchapracticalandeasilyavailablesubstance,isit?Second,usinghydrogenwouldnotsolvethepollutionproblemsassociatedwithcars.Why?Producingpurehydrogencreatesalotofpollution.Togetpurehydrogenfromwaterornaturalgaszyo
9、uhavetouseapurificationprocessthatrequireslotsofenergythatsobtainedbyburningcoaloroil.Andburningcoalandoilcreateslotsofpollution.Soalthoughthecarswouldnotpollute,thefactoriesthatgeneratedthehydrogenforthecarswouldpollute.Thirdztherewontnecessarilybeanycostsavingswhenyouconsiderhowexpensiveitistomanu
10、facturethefuel-cellengine.Thatsbecausefuel-cellenginesrequirecomponentsmadeofplatinum,averyrareandexpensivemetal.Withouttheplatinumcomponentsintheengine,thehydrogendoesntundergothechemicalreactionthatproducestheelectricitytopowertheautomobile.Alltheeffortstoreplaceplatinumwithacheapermaterialhavesof
11、arbeenunsuccessful.阅读听力要点概括ReadingPassageMainpoints:Fuel-cellhaveseveraladvantagesoverinternalcombustionengines.Subpoint1:Internal-combustionreliesonpetroleumandHydrogeniscleanandrenewable.Subpoint2:Fullcellscansolvepollutionproblems.Subpoint3:Full-cellsooncanbeeconomicallycompetitive.LectureAttitud
12、e:Ristoooptimistic.(Hydrogen-basedfull-cellisnotthesolution.)SubPoint1:Hydrogennoteasilyavailable.(Needinapureliquidstate,needverycoldtemperature.)SubPoint2:Hydrogendoesnotsolvethepollution.(Producingcreatesalotofpollution,Burningcoaloroil.)SubPoint3:Nocostsavingsinceexpensivetomanufacture.(Requirep
13、latinum,expensive.)范文逐段贯析Paragraph1Thelecturerpointsoutseveralproblemswiththeuseofhydrogen-basedfuel-cellengineswhichsupportherclaimthatsubstitutingthemforinternal-combustionenginesistechnologicallyunfeasible,environmentallyunfriendly,andeconomicallyunviable.此段功能：(Listeningpassage后文提到用L代替)(Readingpa
14、ssage后文用R代替)开头段作者总结到L指出（氢燃料电池引擎）替换（内燃机引擎）科技上不能实现，环境上不友好，而且经济上不合适。此段结构：这一句话，巧妙的用L的反对逻辑，引出了论证问题的三个方面。把总结L,总结R和表明逻辑轻巧的锁在了一句话里。Paragraph2Firstzthelecturerstatesthatitisimpracticaltoreplaceinternalcombustionengineswithfuel-cellenginesbecauseusingthelatterrequireshydrogeninapureliquidformzwhichistechnolog
15、icallychallengingtobothobtainandstore.However,thereadingpassagearguesthatbecausehydrogencanbeextractedfrommanysourcesincludingwater,fuel-cellenginespoweredbythisinfinitesourceofenergyareanextremelyattractivealternative.此段功能：在第一点technologyunfeasible的论证上。作者复述L觉得电池替换内燃是不现实的，因为电池需要液态氢,而液态氢非常难制取和储存。在R里，R
16、只想到了氢气可以从很多来源从提炼比如水，所以认为燃料是无限的，这种想法很有吸引力。此段结构：此段为分总结构，作者先阐明L认为这个替换是不现实的，因为某些原因。第二句中作者复述了R本来认为的观点，作为对比。Paragraph3Second,thelecturerrefutestheclaiminthereadingthathydrogencellsareenvironmentallyfriendly.Shearguesthatalthoughenginesthatusehydrogencellsproducelesspollution,themanufacturingofhydrogencell
17、sgenerateslargeamountsofharmfulby-productsduetotheburningoffossilfuelsinthepurificationprocess.此段功能：在第二点environmentalunfriendly辩论上，作者直接陈述L认为R所说的电池很环保是错误的。L解释虽然电池引擎不会产生太多污染,但是制造电池引擎的提纯过程消耗了大量的化石燃料也是不环保的。此段结构：此段为总分结构。作者大略总结了一下R的观点并说L持反对意见，随后列举所有的反对R的证据。Paragraph4Thirdzalthoughthereadingsuggeststhathyd
18、rogen-basedenginesaremorefuel-efficientandthuseconomicallycompetitivethaninternal-combustionengines,thelecturerarguesthatsuchanadvantageisunderminedbythefactthatfuel-cellenginesareextremelyexpensivetomanufacture,requiringtheadditionofplatinum,averyrareandexpensivematerial.此段功能：在最后一点economicallyunvia
19、ble的论证上。作者说，虽然R认为电池引擎的燃料效率比内燃机高，但是L举出制造电池引擎需要用到粕这种贵金属，使得其燃料优势被抵消了。此段结构：此段为分分结构，用了一个although,先引出R的论点，再举一系列L的证据来反斥R的论点,达到了反驳的效果。范文全篇总评L逻辑结构全文遵从总分结构，开头段一个难度不高的长句，很好的揉合了逻辑关系，LR双方观点和告诉了读者接下来三个分段的主题。在分论段的论述中，作者很好的陈述了双方观点，根据反对逻辑关系，列出双方的针对证据，结构清晰。2、语言表达本文难度主要来自生词，但是作者用词准确，其中可以借鉴的词句有:Thelecturer/pointsoutseveralProblemS（表达反对关系）/with/theuseofhydrogen-basedfuelcellengines（论文主要事件）/whichsupportherclaimthat/substitutingthemforinternalcombustionengines（B的意见）/is/technologicallyunfeasible,environmentallyunfriendly,andeconomicallyIInViabIe.（三个分论点）/Unfeasible:行不通的Unviable:不能独立的。
