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时间:2020-05-05
《新概念英语第四册第十七单元语法和句型(教学用).doc》由会员上传分享,免费在线阅读,更多相关内容在行业资料-天天文库。
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
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