大学英语四级模拟试题13.docx

大学英语四级模拟试题13.docx

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大学英语四级模拟试题13

大学英语四级模拟试题（13）

一、快速阅读

　　Ifitweren’tfornicotine,peoplewouldn’tsmoketobacco.Why?

Becauseofthemorethan4000chemicalsintobaccosmoke,nicotineistheprimaryonethatactsonthebrain,alteringpeople’smoods,appetitesandalertnessinwaystheyfindpleasantandbeneficial.Unfortunately,asitiswidelyknown,nicotinehasadarkside:

itishighlyaddictive.Oncesmokersbecomehookedonit,theymustgettheirfixofitregularly,sometimesseveraldozentimesaday.Cigarettesmokecontains43knowncarcinogens,whichmeansthatlong-termsmokingcanamounttoadeathsentence.IntheUSalone,420,000Americansdieeveryyearfromtobacco-relatedillnesses.

　　Breakingnicotineaddictionisnoteasy.Eachyear,nearly35millionpeoplemakeaconcertedefforttoquitsmoking.Sadly,lessthan7percentsucceedinabstainingformorethanayear;moststartsmokingagainwithindays.Sowhatisnicotineandhowdoesitinsinuateitselfintothesmoker’sbrainandverybeing?

　　Thenicotinefoundintobaccoisapotentdrugandsmokers,andevensomescientists,sayitofferscertainbenefits.Oneisenhanceperformance.Onestudyfoundthatnon-smokersgivendosesofnicotinetypedabout5percentfasterthantheydidwithoutit.Togreaterorlesserdegrees,usersalsosaynicotinehelpsthemtomaintainconcentration,reduceanxiety,relievepain,andevendampentheirappetites（thushelpinginweightcontrol）.Unfortunately,nicotinecanalsoproducedeleteriouseffectsbeyondaddiction.Athighdoses,asareachievedfromtobaccoproducts,itcancausehighbloodpressure,distressintherespiratoryandgastrointestinalsystemsandanincreaseinsusceptibilitytoseizuresandhypothermia.

　　Firstisolatedasacompoundin1828,initspureformnicotineisaclearliquidthatturnsbrownwhenburnedandsmellsliketobaccowhenexposedtoair.Itisfoundinseveralspeciesofplants,includingtobaccoand,perhapssurprisingly,intomatoes,potatoes,andeggplant（thoughinextremelylowquantitiesthatarepharmacologicallyinsignificantforhumans）.

　　Assimpleasitlooks,thecigaretteishighlyengineerednicotinedeliverydevice.Forinstance,whentobaccoresearchersfoundthatmuchofthenicotineinacigarettewasn’treleasedwhenburnedbutratherremainedchemicallyboundwithinthetobaccoleaf,theybeganaddingsubstancessuchasammoniatocigarettetobaccotoreleasemorenicotine.Ammoniahelpskeepnicotineinitsbasicform,whichismorereadilyvaporisedbytheintenseheatoftheburningcigarettethantheacidicform.MostcigarettesforsaleintheUStodaycontain10milligramsormoreofnicotine.Byinhalingsmokefromalightedcigarette,theaveragesmokertakes1or2milligramsofvaporisednicotinepercigarette.Todayweknowthatonlyaminisculeamountofnicotineisneededtofueladdiction.Researchshowsthatmanufacturerswouldhavetocutnicotinelevelsinatypicalcigaretteby95%toforestallitspowertoaddict.Whenasmokerpuffsonalightedcigarette,smoke,includingvaporisednicotine,isdrawnintothemouth.Theskinandliningofthemouthimmediatelyabsorbsomenicotine,buttheremainderflowsstraightdownintothelungs,whereiteasilydiffusesintothebloodvesselsliningthelungwalls.Thebloodvesselscarrythenicotinetotheheart,whichthenpumpsitdirectlytothebrain.Whilemostoftheeffectsasmokerseeksoccurinthebrain,thehearttakesahitaswell.Studieshaveshownthatasmoker’sfirstcigaretteofthedaycanincreasehisorherheartrateby10to20beatsaminute.Scientistshavefoundthatasmokedsubstancereachesthebrainmorequicklythanoneswallowed,snorted（suchascocainepowder）oreveninjected.Indeed,anicotinemoleculeinhaledinsmokewillreachthebrainwithin10seconds.Thenicotinetravelsthroughbloodvessels,whichbranchoutintocapillarieswithinthebrain.Capillariesnormallycarrynutrientsbuttheyreadilyaccommodatenicotinemoleculesaswell.Onceinsidethebrain,nicotine,likemostaddictivedrugs,triggersthereleaseofchemicalsassociatedwitheuphoriaandpleasure.

　　Justasitmovesrapidlyfromthelungsintothebloodstream,nicotinealsoeasilydiffusesthroughcapillarywalls.Itthenmigratestothespacessurroundingneurones–ganglioncellsthattransmitnerveimpulsesthroughoutthenervoussystem.Theseimpulsesarethebasisforourthoughts,feelings,andmoods.Totransmitnerveimpulsestoitsneighbour,aneuronereleaseschemicalmessengersknownasneurotransmitters.Likenicotinemolecules,theneurotransmittersdriftintotheso-calledsynapticspacebetweenneurones,readytolatchontothereceivingneuroneandthusdeliverachemical“message”thattriggersanelectricalimpulse.

　　Theneurotransmittersbindontoreceptorsonthesurfaceoftherecipientneurone.Thisopenschannelsinthecellsurfacethroughwhichenterions,orchargedatoms,ofsodium.Thisgeneratesacurrentacrossthemembraneofthereceivingcell,whichcompletesdeliveryofthe“message”.Anaccomplishedmimic,nicotinecompeteswiththeneurotransmitterstobindtothereceptors.Itwinsand,likethevanquishedchemical,opensionchannelsthatletsodiumionsintothecell.Butthere’salotmorenicotinearoundthantheoriginaltransmitter,soamuchlargercurrentspreadsacrossthemembrane.Thisbiggercurrentcausesincreasedelectricalimpulsestotravelalongcertainneurones.Withrepeatedsmoking,theneuronesadapttothisincreasedelectricalactivity,andthesmokerbecomesdependentonthenicotine.

　　Questions1–7

　　1.Althoughnicotineisprobablythewell-knownchemicalincigarettes,itisnotnecessarilytheonethatchangesthepsycheofthesmokerwhencigarettesaresmoked.

　　2.Inspiteofthedifficulties,accordingtothetextmorethanthirty-fivemillionpeopleayeargiveupsmoking.

　　3.Ithasbeenshownthatnicotineincigarettescanimprovepeople’sabilitiestoperformsomeactionsmorequickly.

　　4.Addedammoniaincigarettesallowssmokerstoinhalemorenicotine.

　　5.Snortedsubstancesreachthebrainfasterthaninjectedsubstances.

　　6.Nicotinedilatesthebloodvesselsthatcarryitaroundthebody.

　　7.Nicotinemoleculesallowgreaterelectricalchargestopassbetweenneurones.

　　Questions8-10

　　8.Cigarettecompanieswouldhavetocutthenicotinecontentincigarettesby_________topreventthemfrombeingaddictive.

　　9.Accordingtothepassage,acigarettecanraiseasmoker’sheartrateby_________aminute.

　　10.Inordertotransmitnerveimpulsestoitsneighbour,aneuronesends_________knownasneurotransmitters.

二、长对话

　　Conversation1

　　19.（A）Twodifferenttypesofbonesinthehumanbody.

　　（B）Howboneshelpthebodymove.

　　（C）Howbonescontinuouslyrepairthemselves.

　　（D）Thechemicalcompositionofhumanbones.

　　20.（A）Theydefendtheboneagainstviruses.

　　（B）Theypreventoxygenfromenteringthebone.

　　（C）Theybreakdownbonetissue.

　　（D）Theyconnectthebonetomuscletissue.

　　21.（A）Theyhavedifficultyidentifyingthesecells.

　　（B）Theyaren'tsurehowthesecellswork.

　　（C）They'velearnedhowtoreproducethesecells.

　　（D）They'vefoundsimilarcellsinotherspecies.

　　22.（A）Tolearnhowtopreventabonedisease.

　　（B）Tounderstanddifferencesbetweenbonetissueandothertissue.

　　（C）Tofindouthowspecializedbonecellshaveevolved.

　　（D）Tocreateartificialbonetissue.

　　Conversation2

　　23.（A）Anewfuelforbuses.

　　（B）Thecausesofairpollution.

　　（C）Awaytoimprovefuelefficiencyinbuses.

　　（D）Careersinenvironmentalengineering.

　　24.（A）Hercarisbeingrepaired.

　　（B）Shewantstohelpreducepollution.

　　（C）Parkingisdifficultinthecity.

　　（D）Thecostoffuelhasincreased.

　　25.（A）Afuelthatbumscleanly.

　　（B）Anoiladditivethathelpscoolengines.

　　（C）Amaterialfromwhichfiltersaremade.

　　（D）Aninsulatingmaterialsprayedonengineparts.

　三、选词填空

　　Thebiggestsafetythreatfacingairlinestodaymaynotbeaterroristwithagun,butthemanwiththe1computerinbusinessclass.Inthelast15years,pilotshavereportedwellover1002thatcouldhavebeencausedbyelectromagneticinterference.Thesourceofthisinterference3unconfirmed,butincreasingly,expertsarepointingtheblameatportableelectronicdevicesuchasportablecomputers,radioandcassetteplayersandmobiletelephones.

　　RTCA,anorganizationwhichadvisestheaviation（航空）industry,hasrecommendedthatallairlinesban（禁止）suchdevicesfrombeingusedduring“4”stagesofflight,5take-offandlanding.Someexpertshavegonefurther,callingforatotalbanduringallflights.Currently,rulesonusingthesedevicesareleftuptoindividualairlines.Andalthoughsomeairlinesprohibitpassengersfromusingsuchequipmentduringtake-offandlanding,mostare6toenforceatotalban,giventhatmanypassengerswanttoworkduringflights.

　　Thedifficultyis7howelectromagneticfieldsmightaffectanaircraft’scomputers.Expertsknowthatportabledeviceemitradiationwhich8thosewavelengthswhichaircraftusefornavigationandcommunication.But,becausetheyhavenotbeenabletoreproducetheseeffectsinalaboratory,theyhavenowayofknowingwhethertheinterferencemightbedangerousornot.

　　Thefactthataircraftmaybevulnerable（易受损的）tointerferenceraisestheriskthatterroristsmayuseradiosystemsinordertodamagenavigation9.Asworrying,though,isthepassengerwhocan’theartheinstructionstoturnoffhisradiobecausethemusic’stoo10.

　　A）definite

　　B）incidents

　　C）effects

　　D）remains

　　E）critical

　　F）particularly

　　G）reluctant

　　H）refreshing

　　I）portable

　　J）enormou