新概念四Lesson20SnakePoison市公开课金奖市赛课一等奖课件

第1页Lesson20SnakepoisonHowitcameaboutthatsnakesmanufacturedpoisonisamystery．Overtheperiods经过很长时间，在……期间，在……过程中

theirsaliva,amild,digestivejuicelikeourown,wasconvertedinto改变成apoisonthatdefiesanalysiseventoday．Thesolarcellcanconverttheenergyofsunlightintoelectricenergy.第2页Itwasnotforcedupon把……强加给某人

thembythesurvivalcompetition;theycouldhavecaughtandlivedon（注：liveon后面不可跟sb.liveoff后面能够跟sb或sth，意思分别是“靠什么人养活”和“靠什么活着”。）

preywithoutusingpoison含蓄条件句,justas方式状语从句thethousandsofnon-poisonoussnakesstilldo．Poisontoasnakeismerelyaluxury;itenablesittogetitsfoodwithverylittleeffort,nomoreeffortthanonebite同位语．

第3页Andwhyonlysnakes?Cats,forinstance,（省略iftheyhadpoison，含蓄条件句）wouldbegreatlyhelped;norunningfightswithlarge,fierceratsortussleswithgrownrabbits----justabiteandnomoreeffortneeded．

rat第4页Infact,itwouldbeanassistancetoallcarnivoresthoughitwouldbeatwo-edgedweapon一把双刃剑（也可说成double-edgedsword）

whentheyfoughteachother．例句：Scientificdevelopmentmaybeatwo-edgedweapon,ononehanditliftspeople'slivingstandard,ontheotherhanditposespotentialthreatstotheenvironment.

第5页But,of（among）thevertebrates,unpredictableNatureselectedonlysnakes(andonelizard)．OnewondersalsowhyNature,withsomesnakes,concoctedpoisonofsuchextremepotency.

第6页Intheconversionofsalivaintopoison,onemightsuppose（某种可能性）thatafixedprocesstookplace．Itdidnot;somesnakesmanufacturedapoisondifferentineveryrespect在各个方面fromthatofothers,（asdifferentasarsenicisfromstrychnine,andhavingdifferenteffects．）第7页arsenicPoisnouseffectofarsenicArsenicoccursinmanyminerals,mainlycombinedwithsulfur硫磺andmetals,andalsonaturallyinthenative(elemental)state.Strychnineisaverytoxic,colorlesscrystallinealkaloid['ælkəlɔid]n.生物碱)usedasapesticide,particularlyforkillingsmallvertebratessuchasbirdsandrodents啮齿动物

.第8页Onepoisonactsonthenerves,theother（act）ontheblood．acton，对……起作用；遵照。

①Ifaforceorsubstanceactsonsomeoneorsomething,ithasacertaineffectonthem.例句：Thesemedicalherbsaresaidtoactontheheart.

第9页Themakersofthenervepoisonincludethemambasandthecobrasandtheirvenomiscalledneurotoxic．

②Ifyouactonadviceorinformation,youdowhathasbeenadvisedorsuggested.例句：Apatientwillusuallylistentothedoctor'sadviceandactonit.

第10页Vipers(adders)andrattlesnakesmanufacturethebloodpoison,whichisknownashaemolytic．Viper/adderrattlesnake第11页Neurotoxicpoisoneffect第12页Haemolyticpoisoneffect第13页Bothpoisonsareunpleasant,butbyfar（得多，显然：修饰比较级或者最高级）themoreunpleasantisthebloodpoison．例句：Itisquickerbyfartogobytrain.

Itissaidthatthenervepoisonisthemoreprimitiveofthetwo,

第14页thatthebloodpoisonis,sotospeak“能够这么说”，“打个比喻说”,anewerproductfromanimprovedformula．Bethatasitmay倒装让步状语从句，相当于howeverthatmaybe，可译成“尽管如此”,thenervepoisondoesitsbusinesswithman在人身上发挥作用，要人命farmorequicklythanthebloodpoison．

doone’sbusiness

产生效果，完成某人工作第15页This,however,meansnothing．Snakes