英语四级考试阅读基础训练附答案英语四级考试阅读基础训练附答案Nopleasurewithoutpain.以下是小编为大家搜索整理的英语四级考试阅读基础训练附答案，希望能给大家带来帮助!更多精彩内容请及时关注我们应届毕业生考试网!Whenweanalyzethesaltsalinity(盐浓度)ofoceanwaters,wefindthatitvariesonlyslightlyfromplacetoplace.Nevertheless,someofthesesmallchangesareimportant.Therearethreebasicprocessesthatcauseachangeinoceanicsalinity.Oneoftheseisthesubtractionofwaterfromtheoceanbymeansofevaporation.Inthismanner,thesalinityisincreased,sincethesaltstaysbehind.Ifthisiscarriedtotheextreme,ofcourse,whitesaltwouldbeleftbehind;this,bytheway,ishowmuchofthetablesaltweuseisactuallyobtained.Theoppositeofevaporationisprecipitation,suchasrain,bywhichwaterisaddedtotheocean.Heretheoceanisbeingdiluted(稀释)sothatthesalinityisdecreased.Thismayoccurinareasofhighrainfallorincoastalregionswhereriversflowintotheocean.Thussalinitymaybeincreasedbythesubtractionofwaterbyevaporation,ordecreasedbytheadditionoffreshwaterbyprecipitation.Normally,inhotregionswherethesunisverystrong,theoceansalinityissomewhathigherthanitisinotherpartsoftheworldwherethereisnotasmuchevaporation.Similarly,incoastalregionswhereriversdilutethesea,salinityissomewhatlowerthaninotheroceanicareas.Athirdprocessbywhichsalinitymaybealteredisassociatedwiththeformationandmeltingofseaice.Whenseawaterisfrozen,thedissolvedmaterialsareleftbehind..Inthismanner,seawaterdirectlybeneathfreshlyformedseaicehasahighersalinitythanitdidbeforetheiceappeared.Ofcourse,whenthisicemelts,itwilltendtodecreasethesalinityofthesurroundingwater.IntheWeddellSea,thedensestwaterintheoceanisformedasaresultofthisfreezingprocess,whichincreasesthesalinityofcoldwater.Thisheavywatersinksandisfoundinthedeeperportionoftheoceansoftheworld.26.Thispassagemainlytellsusabout_______.A.theanalysisofthesalinityofoceanwatersB.thecausesofthevariationinoceanicsalinityC.theimportanceofthechangesinoceanicsalinityD.thedifferentformsofsaltsinoceanwaters27.Itcanbeknownfromthepassagethatincreaseinthesalinityofoceanwateriscausedby______.A.meltingofseaiceB.precipitationC.evaporationD.supplementof