大学英语四级考试试题Word文档下载推荐.docx

大学英语四级考试试题Word文档下载推荐.docx

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大学英语四级考试试题@#@2011年下半年大学英语四级全真预测模拟题一（配答案解析）@#@01-1Part@#@01-2ⅠWriting（30minutes）Directions:

@#@Forthispart,youareallowed30minutestowriteashortessayentitledThePopularityofGettingCertificatesonCampus.Youshouldwriteatleast150wordsfollowingtheoutlinegivenbelow.@#@01-31.大学校园内各种证书的报考十分火热@#@01-42.大学生考证的利弊@#@01-53.考证面前，我的选择@#@01-6ThePopularityofGettingCertificatesonCampusPartⅡReadingComprehension（SkimmingandScanning）（15minutes）Directions:

@#@Inthispart,youwillhave15minutestogooverthepassagequicklyandanswerthequestionsonAnswerSheet1.Forquestions1-7,choosethebestanswerfromthefourchoicesmarkedA）,B）,C）andD）.Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.MainEnergiesfortheBodyAbalanceddietisonethatprovidesanadequateintakeofenergyandnutrientsformaintenanceofthebodyandthereforegoodhealth.Adietcaneasilybeadequatefornormalbodilyfunctioning,yetmaynotbeabalanceddiet.CarbohydratesCarbohydratesarearapidsourceofenergy,theyarethebody'@#@sfuel.Thebulkofabalanceddietshouldbemadefromcarbohydrates.Ifeateninanexcessofthedietaryrequirementscarbohydratesareeasilystoredasfatsinthecells,althoughcarbohydrateisthefirstsourceofenergyinthebody.Anaverageadultrequiresabout12,000kJofenergyaday,mostofthisissuppliedbytherespirationofcarbohydratesinthecells.Carbohydratesareusedprincipallyasarespiratorysubstrates,i.e.tobeoxidizedtoreleaseenergyforactivetransport,macromoleculesynthesis,celldivisionandmusclecontraction.Carbohydratesaredigestedintheduodenumandileumandabsorbedasglucoseintocells.Sourcesofcarbohydratessuchasstarcharerice,potatoes,wheatandothercereals.Sugarsarealsocarbohydrates,sourcesofsugarsarerefinedsugar-sucrose,whichisafoodsweetenerandpreservativeandfruitsugars-fructose.Ifthedietlackscarbohydratestoresoffataremobilizedandusedasanenergysource.ProteinsProteinisnotadirectsourceofenergyinthebody,itisusedprimarilyforgrowthandrepairofbodytissueswhileremaininganenergysourceasalastresort.Proteinsfulfillawidevarietyofrolesinthebody.Theyarebrokendowninthestomachandintestinestoaminoacidswhicharethenabsorbed.Thebodycanonlyform8aminoacidstobuildproteinsfrom,thedietmustprovideEssentialAminoAcids（EAAs）whicharesynthesizedintoproteinswhichcanbestructural,i.e.collageninbone,keratininhair,myosinandactininmuscle;@#@metabolicenzymes,hemoglobin,protectiveantibodiesandcommunicativehormones.Sourcesofproteinincludemeat,fish,eggsandpulses.Thedietneedstoprovide8EAAsasthebodyisunabletosynthesisproteinswithoutthesemolecules.2otheraminoacidsaresynthesizedfromEAAssoifthedietlackstheoriginalEAAstheseothertwowillnotbepresenteither.Phenylalanineisconvertedtotyrosineandmethionineisconvertedtocysteine.Cellsdrawuponapoolofaminoacidsforproteinsynthesiswhicheithercomefromdietaryproteindigestedandabsorbedinthegutandthebreakdownofbodyproteinsuchasmuscle.However,unlikefatsandcarbohydratesthereisnostoreofaminoacidsforcellstodrawon,anyaminoacidinexcessofimmediatebodilyrequirementsisbrokendownintoureaandexcreted.Itisthereforeimportanttomaintainthedietaryintakeofproteineveryday.Ifthebodylacksprotein,musclewastingoccursasmuscleisbrokendown.Ifproteinislackedinadietapersondevelopskwashiorkorwhichiscausedwhenhighlevelsofcarbohydratesareeatentoovercomethelackofproteininthediet.Onesymptomofkwashiorkoristheabnormalcollectionoffluidaroundtheabdomenduetothelackofproteinintheblood.Thebodycannotretainwaterbyosmosisandfluidaccumulatesintissuescausingthemtobecomewaterlogged.VitaminCategoriesVitaminscannotbesynthesizedbythebodysomustbesuppliedbydiet.Vitaminshavenocommonstructureorfunctionbutareessentialinsmallamountsforthebodytobeabletoutilizeotherdietarycomponentsefficiently.Vitaminsfallintotwocategories,fatsolublevitaminssuchasvitaminA,D,EandKwhichareingestedwithfattyfoodsandwatersolublevitaminssuchastheBgroupvitaminsandvitaminC.Vitaminsareknownasmicronutrientsbecauseonlysmallquantitiesarerequiredforahealthydiet,infactfatsolublevitaminscanbetoxicinhighconcentrations,forexamplethebodystoresvitaminA,orretinol,intheliverasitistoxicifkeptinhighconcentrationsinthebloodstream,adoseofmorethan3300mgofvitaminAcanbeconsideredtoxic.WatersolublevitaminssuchasvitaminCandBgroupsvitaminscanbeexcretedintheurineifinexcessinthediet.VitaminsAVitaminAisessentialtotheproperfunctioningoftheretinaintheeyeandtheepithelialtissues.AlackofvitaminAresultsindry,roughskin,inflammationoftheeyes,adryingorscarringofthecornea-xerophthalmia,whichoccurswhenthesecretionoflubricatingtearsisstopped,theeyelidsbecomeswollenandstickywithpus.Mucoussurfacesoftheeyemaybecomeerodedallowinginfectiontosetin,leadingtoulcerationanddestructionofthecornea.Nightblindness-aninabilitytoseeindimlightcanalsooccur.Rodcellsintheretinaoftheeyedetectlightoflowintensity,theyconvertvitaminAintoapigment,rhodopsin,whichisbleachedwhenlightenterstheeye.Rodcellsresynthesisrhodopsin,butifthereisadeficiencyofthevitamin,rodcellscannolongerfunctionandtheresultisnightblindness.Epithelialcellsuseretinoltomakeretinoicacid,anintracellularmessengerusedincelldifferentiationandgrowth.Withoutretinoicacidepithelialcellsarenotmaintainedproperlyandthebodybecomessusceptibletoinfections,particularlymeaslesandinfectionsoftherespiratorysystemandgut.Xenophthalmiaiscommonamongchildrenwho'@#@sdietsconsistofmainlycerealswithlittlemeatorfreshvegetables,thisiscommoninIndonesia,Bangladesh,IndiaandthePhilippines.VitaminsDVitaminD,orcalciferol,isanotherfatsolublesteroidvitaminwhichfunctionstostimulatecalciumuptakefromthegutanditsdepositioninbone.vitaminDactsasahormonewhenconvertedbyenzymesinthegutandliverintoanactiveformof"@#@activevitaminD"@#@,whichstimulatesepithelialcellsintheintestinetoabsorbcalcium.vitaminDisthereforeessentialingrowingchildren'@#@sdietstoenablethegrowthofstrongbones.WithoutadequateamountsofvitaminDchildrencandeveloprickets,whichisthedeformationofthelegscausedwhentheylackcalciumtostrengthenthebones.InadultsalackofvitaminDinthedietcanleadtoosteomalacia,aprogressivesofteningoftheboneswhichcanmakethemhighlysusceptibletofracture.VitaminDismadebythebodywhenexposedtosunlightandisstoredinthemuscles,however,iftheskinisrarelyexposedtothesunlightorisdarklittlevitaminDisproduced.FoodssuchaseggsandoilyfishareallrichinvitaminD.VitaminsKVitaminK,phylloquinone,isfoundindarkgreenleafyvegetablessuchasspinachandkale.Itisafatsolublevitaminwhichisinvolvedintheclottingprocessofblood.IntheintestinesbacteriasynthesizeanumberofimportantclottingfactorswhichneedvitaminK.WithoutvitaminKcutscanfailtohealandinternalbleedingcanoccur.VitaminsCVitaminCisawatersolublevitamin,knownchemicallyasascorbicacid.Itisfoundincitrusfruitssuchasorangesandlemons,andalsoinpotatoesandtomatoes.ThemainfunctionofvitaminCistheformationofconnectivetissuessuchascollagen.Itisalsoknowntobeanantioxidantwhichhelpstoremovetoxinsandaidstheimmunesystem.AlackofvitaminCleadstoScurvy,aconditionexperiencedbysailorsonlongjourneyswhentheydidnothavefruitintheirdiets.Scurvycausespainful,bleedinggums.AsvitaminCiswatersoluble,itisnottoxicinhighdosesasitcanbeexcretedintheurine,veryhighdosescanhowevercausediarrhea.VitaminsBBgroupvitaminshaveawiderangeofrolesactingasco-enzymesinmetabolicpathways.Theyarefoundinmostplantandanimaltissuesinvolvedinmetabolism,thereforefoodssuchasliver,yeastanddairyproductsareallrichinBgroupvitamins.DeficiencyofBgroupvitaminsincludedermatitis,fatigueandmalformationofredbloodcells.1.Anadultneedsabout12,000kJofenergyadayfrom________.A.thecellB.therespiringprocessofcarbohydratesC.fatsinthecellD.abalanceddiet2.Carbohydratesareultimatelyabsorbedintocellsintheprocessof_______.A.digestionB.respirationC.oxidizationD.mobilization3.TheEssentialAminoAcidswhichbuildpartofproteinscanbeobtainedfrom______.A.stomachB.bodytissuesC.thebodyD.thediet4.Theultimatecauseofkwashiorkorislackof________.A.proteinB.carbohydratesC.vitaminsD.diet5.Vitaminsarecalled“micronutrients”inthat_________.A.excessivefatsolublevitaminscanbeexcretedintheurineB.thebodyonlyrequiressmallamountofvitaminsC.adoseof3300mgofvitaminscanbeconsideredtoxicD.thehighconcentrationsofwatersolublevitaminsaretoxic6.Nightblindnessisadiseasenormallycausedbylackof__________.A.fatsolublevitaminsB.watersolublevitaminsC.vitaminAD.innatedisability7.ThemainfunctionofvitaminDistopreventadultsfrom________.A.thegrowthofstrongbonesB.fractureC.aprogressivesofteningofthebonesD.calciumuptakefromthegut8.AlthoughthehumanbodyproducesvitaminDnormally,itfailstodosoifthereisnotenough______________.9.ThereasonwhyvitaminCisseenasanantioxidanti