新概念英语第四册第十七单元语法和句型(教学用).doc

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1、新概念英语第四册第十七单元语法和句型Lesson17Aman-madedisease人为的疾病IntheearlydaysofthesettlementofAustralia,enterprisingsettlersunwiselyintroducedtheEuropeanrabbit.ThisrabbithadnonaturalenemiesintheAntipodes,sothatitmultipliedwiththatpromiscuousabandoncharacteristicofrabbi

2、ts.Itoverranawholecontinent.Itcauseddevastationbyburrowingandbydevouringtheherbagewhichmighthavemaintainedmillionsofsheepandcattle.Scientistsdiscoveredthatthisparticularvarietyofrabbit(andapparentlynootheranimal)wassusceptibletoafatalvirusdisease,myxoma

3、tosis.Byinfectinganimalsandlettingthemlooseintheburrows,localepidemicsofthisdiseasecouldbecreated.Lateritwasfoundthattherewasatypeofmosquitowhichactedasthecarrierofthisdiseaseandpasseditontotherabbits.Sowhiletherestoftheworldwastryingtogetridofmosquitoe

4、s,Australiawasencouragingthisone.Iteffectivelyspreadthediseasealloverthecontinentanddrasticallyreducedtherabbitpopulation.Itlaterbecameapparentthatrabbitsweredevelopingadegreeofresistancetothisdisease,sothattherabbitpopulationwasunlikelytobecompletelyex

5、terminated.Therewerehopes,however,thattheproblemoftherabbitwouldbecomemanageable.Ironically,Europe,whichhadbequeathedtherabbitasapesttoAustraliaacquiredthisman-madediseaseasapestilence.AFrenchphysiciandecidedtogetridofthewildrabbitsonhisownestateandintr

6、oducedmyxomatosis.Itdidnot,however,remainwithintheconfinesofhisestate.ItspreadthroughFrancewherewildrabbitsarenotgenerallyregardedasapestbutasasportandausefulfoodsupply,anditspreadtoBritainwherewildrabbitsareregardedasapestbutwheredomesticatedrabbits,eq

7、uallysusceptibletothedisease,arethebasisofaprofitablefurindustry.ThequestionbecameoneofwhetherMancouldcontrolthediseasehehadinvented.【语法点】情态动词+完成体不定式【课文原句】Itcauseddevastationbyburrowingandbydevouringtheherbagewhichmighthavemaintainedmillionsofsheepandca

8、ttle.【闯关例句】1.havedonesthmusthavedonesthcanhavedonesthcouldhavedonesthmayhavedonesthmighthavedonesth2.presentstatuspositionmustbeateacher3.bedoingsthmustbewatchingTVpossibilityoughttohavedonesthshouldhavedonesthYoumusthaveleftyour