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1、ReferenceforTeachingⅠ.异域风情PlantsinDesertOnlyspecialplantscansurvivetheterribleclimateofadesert,fortheseareregionswheretheannualrangeofthesoiltemperaturecanbeover75℃.Furthermore,duringthesummertherearefewcloudsintheskytoprotectplantsfromthesun’sray.Anotherproblemisthefactthattherearefrequentlystr
2、ongwindswhichdrivesmall,sharpparticlesofsandintotheplants,tearinganddamagingthem.Themostdifficultproblemforallformsofplantlife,however,isthefactthattheentireannualrainfalloccursduringafewdaysorweeksinspring.Grassesandflowersindesertsurvivefromoneyeartothenextbyexistingthroughthelong,hot,dryseasoni
3、ntheformofseeds.Theseseedsremaininactiveunlesstherightamountofrainfalls.Ifnorainfalls,orifinsufficientrainfalls,theywaituntilthenextyear,orevenstillthenext.Anotherfactorthathelpstheseplantstosurviveisthefactthattheirlifecyclesareshort.Bythetimethatthewaterfromthespringrainsdisappears—justafewweeksa
4、fteritfalls—suchplantsnolongerneedany.Theperennialshavespecialfeatureswhichenablethemtosurviveasplantsforseveralyears.Thus,nearlyalldesertperennialshaveextensiverootsystemsbelowgroundandasmallshootsystemaboveground.Thelargerootnetworkenablestheplanttoabsorbasmuchwateraspossibleinashorttime.Thesmal
5、lshootsystem,ontheotherhand,considerablylimitswaterlossbyevaporation.Anotherfeatureofmanydesertperennialsisthataftertherainyseasontheylosetheirleavesinpreparationforthelong,dryseason,justastreesinwetterclimateslosetheirsinpreparationforthewinter.Thisreducestheirwaterlossbyevaporationduringthedryse
6、ason.Then,inthenextrainyseason,theycomefullyaliveoncemore,andgrownewbranches,leavesandflowers,justasthegrassesandflowersindesertdo.Ⅱ.知识归纳1.accumulate用法归纳(1)积累(vt.)Thescientisthasaccumulatedawealthofexperience.这位科学家已经积累了丰富的经验。(2)堆积，越积越多(vi.）Ifyoudon’tclearawaytherubbishregularly,itwilljustacc
7、umulate.如果你不定时清除垃圾，便会越积越多。Apileofworkaccumulatedonhisdesk.他桌子上有一大堆文件要他处理。2.involve的用法归纳(v.)(1)牵涉，牵连ThiseventinvolvedourinterestsinEurope.这牵涉到我们在欧洲的股份。有时表示“有……参加”。Morethan4millionworkerswereinvolved
