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1、TableofContentPassage12Passage24Passage36Passage49Passage511Passage613Passage715Passage817Passage920Passage1022Passage1123Passage1225Passage1327Passage1428Passage1530Passage1632Passage1734Passage1836Passage1938Passage2039Passage2141Passage2243Passage2
2、345Passage2446Passage2548Passage2649Passage2751Passage2853Passage2955Passage3057Passage3159Passage3262Passage3364Passage3466Passage3567Passage3670Passage3771Passage3872Passage3974Passage4076Passage4177Passage4278Passage4380Passage4481Passage4582Passag
3、e4683Passage4784Passage4886使用说明1、各题答案和解释均隐藏在每篇文章后面，显示的方法是鼠标左键单击“常用”工具栏“显示/隐藏编辑标记”按钮。再次单击又被隐藏。2、试题及答案均经无数遍仔细校对，是官方答案，但错误肯定在所难免。请各位不吝指正，不胜感谢！祝你成功！READINGCOMPREHENSIONPassage1Caffeine,thestimulantincoffee,hasbeencalled“themostwidelyusedpsychoactivesubsta
4、nceonEarth.”Synder,DalyandBrunshaverecentlyproposedthatcaffeineaffectsbehaviorbycounteringtheactivityin(5)thehumanbrainofanaturallyoccurringchemicalcalledadenosine.Adenosinenormallydepressesneuronfiringinmanyareasofthebrain.Itapparentlydoesthisbyinhib
5、itingthereleaseofneurotransmitters,chemicalsthatcarrynerveimpulsesfromoneneurontothenext.(10)Likemanyotheragentsthataffectneuronfiring,adenosinemustfirstbindtospecificreceptorsonneuronalmembranes.Thereareatleasttwoclassesofthesereceptors,whichhavebeen
6、designatedA1andA2.Snyderetalproposethatcaffeine,whichisstruc-(15)turallysimilartoadenosine,isabletobindtobothtypesofreceptors,whichpreventsadenosinefromattachingthereandallowstheneuronstofiremorereadilythantheyotherwisewould.Formanyyears,caffeine’seff
7、ectshavebeenattri-(20)butedtoitsinhibitionoftheproductionofphosphodi-esterase,anenzymethatbreaksdownthechemicalcalledcyclicAMP.AnumberofneurotransmittersexerttheireffectsbyfirstincreasingcyclicAMPconcentra-tionsintargetneurons.Therefore,prolongedperio
8、dsat(25)theelevatedconcentrations,asmightbebroughtaboutbyaphosphodiesteraseinhibitor,couldleadtoagreateramountofneuronfiringand,consequently,tobehav-ioralstimulation.ButSnyderetalpointoutthatthecaffeineconcentrationsneededtoinhibittheproductio
