情态动词表可能性情态动词：may、might.英语中除了情态动词表可能性，还可以用adj或adv:probably，possible.may(可能):暗含不确定的意思。might:表可能，但它的含义比may更不确定。Hemaybeathome.Hemightcomesoon.Itwillprobablybehotandsunny.Must表示主观义务和需要。Mustn’t表示禁止Need也表示需要，但不一定是一种义务，语气没那么强烈。（1）need用作实义动词needtodosth需要做某事肯定句：Heneedstogoshopping.他需要去购物。否定句：Hedoesn'tneedtogoshopping.（实意动词否定都借助助动词do/does）疑问句：Doesheneedtogoshopping?Yes,hedoes.No,hedoesn't.（2）need用作情态动词needdosth需要做某事肯定句：Heneedgoshopping.他需要去购物。否定句：Heneedn'tgoshopping（情态动词否定都直接在后面加not）疑问句：Needhegoshopping?Yes,hemustNoheneedn't（3）must“必须……，得……，要……”；肯定：Youmustgotoschoolontime.你必须按时到校否定：Youneedn'tgotoschoolontime.你不必按时到校。疑问：MustIgotoschoolontime?Yes,youmustNo,youneedn'thaveto与must的区别must侧重于说话者的主观看法，认为有必要或有义务haveto侧重于客观需要，含有“不得不，被迫”之意。e.g.Allpassengersmustwearseatbelts.所有乘客都要系安全带。Mybikewasbrokenyesterday,soIhadtowalktoschool.昨天我的自行车坏了，所以我只能走路去学校。情态动词表示推测的用法:表示肯定推测时，语气由强到弱：Mustbe>Canbe>Couldbe>Maybe>Mightbe注意在推测的过程中，如果句子中已经有动词的话，省略be。所有的否定推测均用can’tbe情态动词练习题()1.John___cometoseeustonight,butheisn'tverysureyet.A.mayB.canC.hastoD.must()2.They___dowellintheexam.A.canbeabletoB.beabletoC.canabletoD.areableto()3.-MayItakethisbookout?-No,you___.A.can'tB.maynotC.needn'tD.aren't()4.You___goandseeadoctoratoncebecauseyou'regotafever.A.canB.mustC.dareD.would()5.-CanyouspeakJapanese?-No,I____.A.mustn'tB.can'tC.needn'tD.maynot()6.-He___beintheclassroom,Ithink.-No,he___beintheclassroom.Isawhimgohomeaminuteago.A.can;maynotB.must;maynotC.may;can'tD.may;mustn't()7.Eventhetopstudentsinourclasscan'tworkoutthisproblem,soit___beverydifficult.A.mayB.mustC.canD.need()8.Heisn'tatschool.Ithinkhe___beill.A.canB.willC.mustD.hasto()9.___Itakethisone?A.MayB.WillC.AreD.Do()10.Thechildren___playfootballontheroad.A.can'tB.canC.mustn'tD.must()11.You___belateforschoolagainnexttime.A.mustn'tB.needn'tC.don'thavetoD.don'tneedto()12.-MustIdomyhomeworkatonce?-No,you___.A.needn'tB.mustn'tC.can'tD.maynot()13.H