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1、大学英语四级新题型模拟训练 一、快速阅读 Ifitweren’tfornicotine,peoplewouldn’tsmoketobacco.Why?Becauseofthemorethan4000chemicalsintobaccosmoke,nicotineistheprimaryonethatactsonthebrain,alteringpeople’smoods,appetitesandalertnessinwaystheyfindpleasantandbeneficial.Unfortunately,asitiswidelyknown,nicotinehasadarksid
2、e:itishighlyaddictive.Oncesmokersbecomehookedonit,theymustgettheirfixofitregularly,sometimesseveraldozentimesaday.Cigarettesmokecontains43knowncarcinogens,whichmeansthatlong-termsmokingcanamounttoadeathsentence.IntheUSalone,420,000Americansdieeveryyearfromtobacco-relatedillnesses. Breakingnicot
3、ineaddictionisnoteasy.Eachyear,nearly35millionpeoplemakeaconcertedefforttoquitsmoking.Sadly,lessthan7percentsucceedinabstainingformorethanayear;moststartsmokingagainwithindays.Sowhatisnicotineandhowdoesitinsinuateitselfintothesmoker’sbrainandverybeing? Thenicotinefoundintobaccoisapotentdrugands
4、mokers,andevensomescientists,sayitofferscertainbenefits.Oneisenhanceperformance.Onestudyfoundthatnon-smokersgivendosesofnicotinetypedabout5percentfasterthantheydidwithoutit.Togreaterorlesserdegrees,usersalsosaynicotinehelpsthemtomaintainconcentration,reduceanxiety,relievepain,andevendampentheira
5、ppetites(thushelpinginweightcontrol).Unfortunately,nicotinecanalsoproducedeleteriouseffectsbeyondaddiction.Athighdoses,asareachievedfromtobaccoproducts,itcancausehighbloodpressure,distressintherespiratoryandgastrointestinalsystemsandanincreaseinsusceptibilitytoseizuresandhypothermia. Firstisola
6、tedasacompoundin1828,initspureformnicotineisaclearliquidthatturnsbrownwhenburnedandsmellsliketobaccowhenexposedtoair.Itisfoundinseveralspeciesofplants,includingtobaccoand,perhapssurprisingly,intomatoes,potatoes,andeggplant(thoughinextremelylowquantitiesthatarepharmacologicallyinsignificantforhum
7、ans). Assimpleasitlooks,thecigaretteishighlyengineerednicotinedeliverydevice.Forinstance,whentobaccoresearchersfoundthatmuchofthenicotineinacigarettewasn’treleasedwhenburnedbutratherremainedchemicallyboundwithinthetobaccole
