最新大学英语四级模拟试题附答案.docx

最新大学英语四级模拟试题附答案.docx

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最新大学英语四级模拟试题附答案

2011最新大学英语四级模拟试题

（一）

PartⅠWriting（30minutes）

　　Directions:

Forthispart,youareallowed30minutestowriteashortessayentitledThePopularityofGettingCertificatesonCampus.Youshouldwriteatleast150wordsfollowingtheoutlinegivenbelow.

　　1.大学校园内各种证书的报考十分火热

　　2.大学生考证的利弊

　　3.考证面前，我的选择

　　ThePopularityofGettingCertificatesonCampus

　　PartⅡReadingComprehension（SkimmingandScanning）（15minutes）

　　Directions:

Inthispart,youwillhave15minutestogooverthepassagequicklyandanswerthequestionsonAnswerSheet1.

　　Forquestions1-7,choosethebestanswerfromthefourchoicesmarkedA）,B）,C）andD）.Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.

　　MainEnergiesfortheBody

　　Abalanceddietisonethatprovidesanadequateintakeofenergyandnutrientsformaintenanceofthebodyandthereforegoodhealth.Adietcaneasilybeadequatefornormalbodilyfunctioning,yetmaynotbeabalanceddiet.

　　Carbohydrates

　　Carbohydratesarearapidsourceofenergy,theyarethebody'sfuel.Thebulkofabalanceddietshouldbemadefromcarbohydrates.Ifeateninanexcessofthedietaryrequirementscarbohydratesareeasilystoredasfatsinthecells,althoughcarbohydrateisthefirstsourceofenergyinthebody.Anaverageadultrequiresabout12,000kJofenergyaday,mostofthisissuppliedbytherespirationofcarbohydratesinthecells.

　　Carbohydratesareusedprincipallyasarespiratorysubstrates,i.e.tobeoxidizedtoreleaseenergyforactivetransport,macromoleculesynthesis,celldivisionandmusclecontraction.Carbohydratesaredigestedintheduodenumandileumandabsorbedasglucoseintocells.Sourcesofcarbohydratessuchasstarcharerice,potatoes,wheatandothercereals.Sugarsarealsocarbohydrates,sourcesofsugarsarerefinedsugar-sucrose,whichisafoodsweetenerandpreservativeandfruitsugars-fructose.Ifthedietlackscarbohydratestoresoffataremobilizedandusedasanenergysource.

　　Proteins

　　Proteinisnotadirectsourceofenergyinthebody,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.

VitaminCategories

　　Vitaminscannotbesynthesizedbythebodysomustbesuppliedbydiet.Vitaminshavenocommonstructureorfunctionbutareessentialinsmallamountsforthebodytobeabletoutilizeotherdietarycomponentsefficiently.

　　Vitaminsfallintotwocategories,fatsolublevitaminssuchasvitaminA,D,EandKwhichareingestedwithfattyfoodsandwatersolublevitaminssuchastheBgroupvitaminsandvitaminC.Vitaminsareknownasmicronutrientsbecauseonlysmallquantitiesarerequiredforahealthydiet,infactfatsolublevitaminscanbetoxicinhighconcentrations,forexamplethebodystoresvitaminA,orretinol,intheliverasitistoxicifkeptinhighconcentrationsinthebloodstream,adoseofmorethan3300mgofvitaminAcanbeconsideredtoxic.WatersolublevitaminssuchasvitaminCandBgroupsvitaminscanbeexcretedintheurineifinexcessinthediet.

　　VitaminsA

　　VitaminAisessentialtotheproperfunctioningoftheretinaintheeyeandtheepithelialtissues.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.

　VitaminsD

　　VitaminD,orcalciferol,isanotherfatsolublesteroidvitaminwhichfunctionstostimulatecalciumuptakefromthegutanditsdepositioninbone.vitaminDactsasahormonewhenconvertedbyenzymesinthegutandliverintoanactiveformof"activevitaminD",whichstimulatesepithelialcellsintheintestinetoabsorbcalcium.vitaminDisthereforeessentialingrowingchildren'sdietstoenablethegrowthofstrongbones.WithoutadequateamountsofvitaminDchildrencandeveloprickets,whichisthedeformationofthelegscausedwhentheylackcalciumtostrengthenthebones.InadultsalackofvitaminDinthedietcanleadtoosteomalacia,aprogressivesofteningoftheboneswhichcanmakethemhighlysusceptibletofracture.

　　VitaminDismadebythebodywhenexposedtosunlightandisstoredinthemuscles,however,iftheskinisrarelyexposedtothesunlightorisdarklittlevitaminDisproduced.FoodssuchaseggsandoilyfishareallrichinvitaminD.

　　VitaminsK

　　VitaminK,phylloquinone,isfoundindarkgreenleafyvegetablessuchasspinachandkale.Itisafatsolublevitaminwhichisinvolvedintheclottingprocessofblood.IntheintestinesbacteriasynthesizeanumberofimportantclottingfactorswhichneedvitaminK.WithoutvitaminKcutscanfailtohealandinternalbleedingcanoccur.

　　VitaminsC

　　VitaminCisawatersolublevitamin,knownchemicallyasascorbicacid.Itisfoundincitrusfruitssuchasorangesandlemons,andalsoinpotatoesandtomatoes.ThemainfunctionofvitaminCistheformationofconnectivetissuessuchascollagen.Itisalsoknowntobeanantioxidantwhichhelpstoremovetoxinsandaidstheimmunesystem.AlackofvitaminCleadstoScurvy,aconditionexperiencedbysailorsonlongjourneyswhentheydidnothavefruitintheirdiets.Scurvycausespainful,bleedinggums.AsvitaminCiswatersoluble,itisnottoxicinhighdosesasitcanbeexcretedintheurine,veryhighdosescanhowevercausediarrhea.

VitaminsB

　　Bgroupvitaminshaveawiderangeofrolesactingasco-enzymesinmetabolicpathways.Theyarefoundinmostplantandanimaltissuesinvolvedinmetabolism,thereforefoodssuchasliver,yeastanddairyproductsareallrichinBgroupvitamins.DeficiencyofBgroupvitaminsincludedermatitis,fatigueandmalformationofredbloodcells.

　　1.Anadultneedsabout12,000kJofenergyadayfrom________.

　　A.thecellB.therespiringprocessofcarbohydrates

　　C.fatsinthecellD.abalanceddiet

　　2.Carbohydratesareultimatelyabsorbedintocellsintheprocessof_______.

　　A.digestionB.respiration

　　C.oxidizationD.mobilization

　　3.TheEssentialAminoAcidswhichbuildpartofproteinscanbeobtainedfrom______.

　　A.stomachB.bodytissues

　　C.thebodyD.thediet

　　4.Theultimatecauseofkwashiorkorislackof________.

　　A.proteinB.carbohydrates

　　C.vitaminsD.diet

　　5.Vitaminsarecalled“micronutrients”inthat_________.

　　A.excessivefatsolublevitaminscanbeexcretedintheurineB.thebodyonlyrequiressmallamountofvitamins

　　C.adoseof3300mgofvitaminscanbeconsideredtoxicD.thehighconcentrationsofwatersolublevitaminsaretoxic

　　6.Nightblindnessisadiseasenormallycausedbylackof__________.

　　A.fatsolublevitaminsB.watersolublevitamins

　　C.vitaminAD.innatedisability

　　7.ThemainfunctionofvitaminDistopreventadultsfrom________.

　　A.thegrowthofstrongbonesB.fracture

　　C.aprogressivesofteningofthebonesD.calciumuptakefromthegut

　　8.AlthoughthehumanbodyproducesvitaminDnormally,i