四级模拟考试题目VIP免费

大学英语四级考试模拟试题PartIWriting(30minutes)Directions:Forthispartyouareallowed30minutestowriteanessaybasedontheoutlinebelow.Youshouldwriteatleast120words，andbaseyourcompositionontheoutlinegivenbelowinChinese.现在社会上越来越多人开始在网上购买商品了，对此你有什么看法呢?1.很多人开始在网上购买商品2.网上购物可能存在的问题3.我的看法TheQualityofProductsPartIIReadingComprehension(SkimmingandScanning)(15minutes)Directions:Inthispart,youwillhave15minutestogooverthepassagequicklyandanswerthequestionsonAnswerSheet1.Forquestions1-7,markY(forYES)ifthestatementagreeswiththeinformationgiveninthepassage;N(forNO)ifthestatementcontradictswiththeinformationgiveninthepassage;NG(forNOTGIVEN)iftheinformationisnotgiveninthepassage;Forquestions8-10,completethesentenceswiththeinformationgiveninthepassage.Oneinthreeofuswillgetcanceratsomepointinourlives.Oncesofeareditsnamewaswhispered,thediseaseisnolongeraninevitabledeathsentence.Today,almosttwo-thirdsofthosewhodevelopcancerwillstillbealivefiveyearslater,comparedwithjusthalfin1970s.CancerhasturnedouttobetoughertocrackthaneveryonehopedwhenU.S.PresidentRichardNixonlaunchedtheWaronCancerin1971.Butdeathratesarefalling,thankstoearlierdetectionoftumors(肿瘤)andimproveduseofexistingtreatments—mainlychemotherapyandradiotherapy.Thesuccesshasbeenbiggestforchildren:sincethemid-1970s,deathratesfromcancersofchildhoodhavehalved.Innerworkings.Akeyreasonwhycancerpatientsarelivinglongeristhatscientistsnowunderstandmoreclearlywhathappenswhencellsturncancerous.Cancerbeginswhengeneswhichnormallycontrolcelldivision,growthandrepairaredamagedthroughmutation(突变).Thesegenescanthencausecellstogrowanddivideuncontrollably,destroyingneighboringhealthycells.MutationscanarisebychanceerrorsinDNAreplication,andgenescanalsobedamagedbycarcinogens(致癌物质)—suchastobaccochemicals,benzene,andsomefoodadditives—orultravioletlightfromsunshine.Certainvirusescanalsotriggergenemutations,suchasthehumanpapilloma(乳突淋瘤)virusthatcancausecervical(子宫颈的)cancer.Somemutatedgenesareinherited:twoexamplesareBRCA1andBRCA2,whichtogetheraccountforabout5%ofallbreastcancercases.OthergenessuchasDBC2,EMSYandFAhavebeenimplicatedinovarian,breastandlungcancer.Onceacellhasturnedcancerous,itdividesuntilamassofcellsformsatumor.Diagnostictestscanquicklydistinguishbetweenmalignant,orcancerous,tumorsandthosethatarebenign,orharmless.Asamalignanttumorprogresses,cellsorclumpsofcellsbreakoffandspread,aroundthebodyviathelymphaticsystemandbloodvessels.Thelatestgenerationoftreatmentsexploitourknowledgeofwhathappenswithincancerouscells.Thesetargetproteinsandmessengerchemicals—suchasgrowthfactorsorenzymes–thattheerrantcellsneedtosurviveandgrow.PrevalencepatternsIndevelopedcountries,thecancermostlikelytoafflictyouisnon-melanomaskincancer,oftencausedbytheSun’sharmfulultravioletrays.Thisisusuallytreatedandcured.Melanoma,adeadlierskincancer,islesscommonbutisincreasingbyaround3%ayearintheU.S.ThoughUVlightisthecauseofmanyskincancers,thereissomeevidencethatsmallamountsmayalsohelppreventothercancers.Inthedevelopingworldthemostcommoncancersarelinkedtoinfectiousagents,suchascervicalcancerorlivercancer,causedbyhepatitis（肝炎）B.Thebiggestkillerinindustrializednationsremainslungcancer.Formen,lungcancermortalityhasbeenfallingsince1990,mirroringapeakinpopularityofsmokingduringthe1960s.Forwomen,whocommonlytookupsmokin...