大学英语四级（CET-4）快速阅读专题强化练习三.docx

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1、大学英语四级（CET-4）快速阅读专题强化练习三想在大学英语四级考试中一举获胜，拿到高分吗？首先攻克快速阅读这一版块，想在短短的15分钟内快速又准确地拿下这一道题，需要你平时的大量练习，培养快速从大量信息中提取要点的能力；这里我们将提供大量的快速阅读专题联系，它们将是你通向成功的得力助手！1Directions:Inthispart,youwillhave15minutestogooverthepassagequicklyForquestions1-7,markY(forYES)ifthestatementagreeswiththeinformationgiveninthepassage;N(

2、forNO)ifhestatementcontradictstheinformationgiveninthepassage;NG(forNOTGIVEN)iftheinformationisnotgiveninthepassage;Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.Ifitweren’tfornicotine,peoplewouldn’tsmoketobacco.Why?Becauseofthemorethan4000chemicalsintobaccosmo

3、ke,nicotineistheprimaryonethatactsonthebrain,alteringpeople’smoods,appetitesandalertnessinwaystheyfindpleasantandbeneficial.Unfortunately,asitiswidelyknown,nicotinehasadarkside:itishighlyaddictive.Oncesmokersbecomehookedonit,theymustgettheirfixofitregularly,sometimesseveraldozentimesaday.Cigar

4、ettesmokecontains43knowncarcinogens,whichmeansthatlong-termsmokingcanamounttoadeathsentence.IntheUSalone,420,000Americansdieeveryyearfromtobacco-relatedillnesses.Breakingnicotineaddictionisnoteasy.Eachyear,nearly35millionpeoplemakeaconcertedefforttoquitsmoking.Sadly,lessthan7percentsucceedinabstaini

5、ngformorethanayear;moststartsmokingagainwithindays.Sowhatisnicotineandhowdoesitinsinuateitselfintothesmoker’sbrainandverybeing?Thenicotinefoundintobaccoisapotentdrugandsmokers,andevensomescientists,sayitofferscertainbenefits.Oneisenhanceperformance.Onestudyfoundthatnon-smokersgivendosesofnicot

6、inetypedabout5percentfasterthantheydidwithoutit.Togreaterorlesserdegrees,usersalsosaynicotinehelpsthemtomaintainconcentration,reduceanxiety,relievepain,andevendampentheirappetites(thushelpinginweightcontrol).Unfortunately,nicotinecanalsoproducedeleteriouseffectsbeyondaddiction.Athighdoses,asareachie

7、vedfromtobaccoproducts,itcancausehighbloodpressure,distressintherespiratoryandgastrointestinalsystemsandanincreaseinsusceptibilitytoseizuresandhypothermia.Firstisolatedasacompoundin1828,initspureformnicotineisaclearliquidthatturnsbrownwhenburnedandsmellsliketobaccowhenexposedtoair.Itisfoundinseveral

8、speciesofplants,includingtobaccoand,perhapssurprisingly,intomatoes,potatoes,andeggplant(thoughinextremelylowquantitiesthatarepharmacologicallyinsignificantforhumans).Assimpleasitlooks,thecigaretteishighlyengineerednicotinedeliverydevice.Forinstance,whentobaccoresearchersfoundthatmuchofthenicotineina

9、cigarettewasn’treleasedwhenburnedbutratherremainedchemicallyboundwithinthetobaccoleaf,theybeganaddingsubstancessuchasammoniatocigarettetobaccotoreleasemorenicotine.Ammoniahelpskeepnicotineinitsbasicform,whichismorereadilyvaporisedbytheintenseheatoftheburningcigarettethantheacidicform.Mostcigar

10、ettesforsaleintheUStodaycontain10milligramsormoreofnicotine.Byinhalingsmokefromalightedcigarette,theaveragesmokertakes1or2milligramsofvaporisednicotinepercigarette.Todayweknowthatonlyaminisculeamountofnicotineisneededtofueladdiction.Researchshowsthatmanufacturerswouldhavetocutnicotinelevelsinatypica

11、lcigaretteby95%toforestallitspowertoaddict.Whenasmokerpuffsonalightedcigarette,smoke,includingvaporisednicotine,isdrawnintothemouth.Theskinandliningofthemouthimmediatelyabsorbsomenicotine,buttheremainderflowsstraightdownintothelungs,whereiteasilydiffusesintothebloodvesselsliningthelungwalls.Theblood

12、vesselscarrythenicotinetotheheart,whichthenpumpsitdirectlytothebrain.Whilemostoftheeffectsasmokerseeksoccurinthebrain,thehearttakesahitaswell.Studieshaveshownthatasmoker’sfirstcigaretteofthedaycanincreasehisorherheartrateby10to20beatsaminute.Scientistshavefoundthatasmokedsubstancereachesthebra

13、inmorequicklythanoneswallowed,snorted(suchascocainepowder)oreveninjected.Indeed,anicotinemoleculeinhaledinsmokewillreachthebrainwithin10seconds.Thenicotinetravelsthroughbloodvessels,whichbranchoutintocapillarieswithinthebrain.Capillariesnormallycarrynutrientsbuttheyreadilyaccommodatenicotinemolecule

14、saswell.Onceinsidethebrain,nicotine,likemostaddictivedrugs,triggersthereleaseofchemicalsassociatedwitheuphoriaandpleasure.Justasitmovesrapidlyfromthelungsintothebloodstream,nicotinealsoeasilydiffusesthroughcapillarywalls.Itthenmigratestothespacessurroundingneurones–ganglioncellsthattransmitner

15、veimpulsesthroughoutthenervoussystem.Theseimpulsesarethebasisforourthoughts,feelings,andmoods.Totransmitnerveimpulsestoitsneighbour,aneuronereleaseschemicalmessengersknownasneurotransmitters.Likenicotinemolecules,theneurotransmittersdriftintotheso-calledsynapticspacebetweenneurones,readytolatchontot

16、hereceivingneuroneandthusdeliverachemicalmessagethattriggersanelectricalimpulse.Theneurotransmittersbindontoreceptorsonthesurfaceoftherecipientneurone.Thisopenschannelsinthecellsurfacethroughwhichenterions,orchargedatoms,ofsodium.Thisgeneratesacurrentacrossthemembraneofthereceivingcell,whichcomplete

17、sdeliveryofthemessage.Anaccomplishedmimic,nicotinecompeteswiththeneurotransmitterstobindtothereceptors.Itwinsand,likethevanquishedchemical,opensionchannelsthatletsodiumionsintothecell.Butthere’salotmorenicotinearoundthantheoriginaltransmitter,soamuchlargercurrentspreadsacrossthemembrane.Thisbi

18、ggercurrentcausesincreasedelectricalimpulsestotravelalongcertainneurones.Withrepeatedsmoking,theneuronesadapttothisincreasedelectricalactivity,andthesmokerbecomesdependentonthenicotine.1.Althoughnicotineisprobablythewell-knownchemicalincigarettes,itisnotnecessarilytheonethatchangesthepsycheofthesmok

19、erwhencigarettesaresmoked.2.Inspiteofthedifficulties,accordingtothetextmorethanthirty-fivemillionpeopleayeargiveupsmoking.3.Ithasbeenshownthatnicotineincigarettescanimprovepeople’sabilitiestoperformsomeactionsmorequickly.4.Addedammoniaincigarettesallowssmokerstoinhalemorenicotine.5.Snortedsubs

20、tancesreachthebrainfasterthaninjectedsubstances.6.Nicotinedilatesthebloodvesselsthatcarryitaroundthebody.7.Nicotinemoleculesallowgreaterelectricalchargestopassbetweenneurones.8.Cigarettecompanieswouldhavetocutthenicotinecontentincigarettesbytopreventthemfrombeingaddictive.9.Accordingtothepassage,acigarettecanraiseasmoker’sheartratebyaminute.10.Inordertotransmitnerveimpulsestoitsneighbour,aneuronesendsknownasneurotransmitters.第7页 共7页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页第 7 页 共 7 页