大学英语四级新题型模拟训练.docx
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大学英语四级新题型模拟训练.docx
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大学英语四级新题型模拟训练
大学英语四级新题型模拟训练
大学英语四级新题型模拟训练大学英语四级新题型模拟训练一、快速阅读ifitwerentfornicotine,peoplewouldntsmoketobacco.why?
becauseofthemorethan4000chemicalsintobaccosmoke,nicotineistheprimaryonethatactsonthebrain,alteringpeoplesmoods,appetitesandalertnessinwaystheyfindpleasantandbeneficial.unfortunately,asitiswidelyknown,nicotinehasadarkside:
itishighlyaddictive.oncesmokersbecomehookedonit,theymustgettheirfixofitregularly,sometimesseveraldozentimesaday.cigarettesmokecontains43knowncarcinogens,whichmeansthatlong-termsmokingcanamounttoadeathsentence.intheusalone,420,000americansdieeveryyearfromtobacco-relatedillnesses.
breakingnicotineaddictionisnoteasy.eachyear,nearly35millionpeoplemakeaconcertedefforttoquitsmoking.sadly,lessthan7percentsucceedinabstainingformorethanayear;moststartsmokingagainwithindays.sowhatisnicotineandhowdoesitinsinuateitselfintothesmokersbrainandverybeing?
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,whentobaccoresearchersfoundthatmuchofthenicotineinacigarettewasntreleasedwhenburnedbutratherremainedchemicallyboundwithinthetobaccoleaf,theybeganaddingsubstancessuchasammoniatocigarettetobaccotoreleasemorenicotine.ammoniahelpskeepnicotineinitsbasicform,whichismorereadilyvaporisedbytheintenseheatoftheburningcigarettethantheacidicform.mostcigarettesforsaleintheustodaycontain10milligramsormoreofnicotine.byinhalingsmokefromalightedcigarette,theaveragesmokertakes1or2milligramsofvaporisednicotinepercigarette.todayweknowthatonlyaminisculeamountofnicotineisneededtofueladdiction.researchshowsthatmanufacturerswouldhavetocutnicotinelevelsinatypicalcigaretteby95%toforestallitspowertoaddict.whenasmokerpuffsonalightedcigarette,smoke,includingvaporisednicotine,isdrawnintothemouth.theskinandliningofthemouthimmediatelyabsorbsomenicotine,buttheremainderflowsstraightdownintothelungs,whereiteasilydiffusesintothebloodvesselsliningthelungwalls.thebloodvesselscarrythenicotinetotheheart,whichthenpumpsitdirectlytothebrain.whilemostoftheeffectsasmokerseeksoccurinthebrain,thehearttakesahitaswell.studieshaveshownthatasmokersfirstcigaretteofthedaycanincreasehisorherheartrateby10to20beatsaminute.scientistshavefoundthatasmokedsubstancereachesthebrainmorequicklythanoneswallowed,snorted(suchascocainepowder)oreveninjected.indeed,anicotinemoleculeinhaledinsmokewillreachthebrainwithin10seconds.thenicotinetravelsthroughbloodvessels,whichbranchoutintocapillarieswithinthebrain.capillariesnormallycarrynutrientsbuttheyreadilyaccommodatenicotinemoleculesaswell.onceinsidethebrain,nicotine,likemostaddictivedrugs,triggersthereleaseofchemicalsassociatedwitheuphoriaandpleasure.
justasitmovesrapidlyfromthelungsintothebloodstream,nicotinealsoeasilydiffusesthroughcapillarywalls.itthenmigratestothespacessurroundingneuronesganglioncellsthattransmitnerveimpulsesthroughoutthenervoussystem.theseimpulsesarethebasisforourthoughts,feelings,andmoods.totransmitnerveimpulsestoitsneighbour,aneuronereleaseschemicalmessengersknownasneurotransmitters.likenicotinemolecules,theneurotransmittersdriftintotheso-calledsynapticspacebetweenneurones,readytolatchontothereceivingneuroneandthusdeliverachemicalmessagethattriggersanelectricalimpulse.
theneurotransmittersbindontoreceptorsonthesurfaceoftherecipientneurone.thisopenschannelsinthecellsurfacethroughwhichenterions,orchargedatoms,ofsodium.thisgeneratesacurrentacrossthemembraneofthereceivingcell,whichcompletesdeliveryofthemessage.anaccomplishedmimic,nicotinecompeteswiththeneurotransmitterstobindtothereceptors.itwinsand,likethevanquishedchemical,opensionchannelsthatletsodiumionsintothecell.buttheresalotmorenicotinearoundthantheoriginaltransmitter,soamuchlargercurrentspreadsacrossthemembrane.thisbiggercurrentcausesincreasedelectricalimpulsestotravelalongcertainneurones.withrepeatedsmoking,theneuronesadapttothisincreasedelectricalactivity,andthesmokerbecomesdependentonthenicotine.
questions17
1.althoughnicotineisprobablythewell-knownchemicalincigarettes,itisnotnecessarilytheonethatchangesthepsycheofthesmokerwhencigarettesaresmoked.
2.inspiteofthedifficulties,accordingtothetextmorethanthirty-fivemillionpeopleayeargiveupsmoking.
3.ithasbeenshownthatnicotineincigarettescanimprovepeoplesabilitiestoperformsomeactionsmorequickly.
4.addedammoniaincigarettesallowssmokerstoinhalemorenicotine.
5.snortedsubstancesreachthebrainfasterthaninjectedsubstances.
6.nicotinedilatesthebloodvesselsthatcarryitaroundthebody.
7.nicotinemoleculesallowgreaterelectricalchargestopassbetweenneurones.
questions8-10
8.cigarettecompanieswouldhavetocutthenicotinecontentincigarettesby_________topreventthemfrombeingaddictive.
9.accordingtothepassage,acigarettecanraiseasmokersheartrateby_________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)suchdevicesfrombeingusedduring4stagesofflight,5take-offandlanding.someexpertshavegonefurther,callingforatotalbanduringallflights.currently,rulesonusingthesedevicesareleftuptoindividualairlines.andalthoughsomeairlinesprohibitpassengersfromusingsuchequipmentduringtake-offandlanding,mostare6toenforceatotalban,giventhatmanypassengerswanttoworkduringflights.
thedifficultyis7howelectromagneticfieldsmightaffectanaircraftscomputers.expertsknowthatportabledeviceemitradiationwhich8thosewavelengthswhichaircraftusefornavigationandcommunication.but,becausetheyhavenotbeenabletoreproducetheseeffectsinalaboratory,theyhavenowayofknowingwhethertheinterferencemightbedangerousornot.
thefactthataircraftmaybevulnerable(易受损的)tointerferenceraisestheriskthatterroristsmayuseradiosystemsinordertodamagenavigation9.asworrying,though,isthepassengerwhocantheartheinstructionstoturnoffhisradiobecausethemusicstoo10.
a)definite
b)incidents
c)effects
d)remains
e)critical
f)particularly
g)reluctant
h)refreshing
i)portable
j)enormous
k)predicting
l)liberal
m)affects
n)equipment
o)loud
四、改错
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