最新大学英语四级模拟试题附答案Word格式.docx
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最新大学英语四级模拟试题附答案Word格式.docx
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2.大学生考证的利弊
3.考证面前,我的选择
ThePopularityofGettingCertificatesonCampus
PartⅡReadingComprehension(SkimmingandScanning)(15minutes)
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
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