一、作主语⒈不定式作主语动词不定式作主语时，句子的谓语动词常用单数，其位置有以下两种：(666)把不定式置于句首。如：Togettherebybikewilltakeushalfanhour.(2)用it作形式主语，把真正的主语不定式置于句后，常用于下列句式中。如：①It＋be＋名词＋todoIt'sourdutytotakegoodcareoftheold.②Ittakessb+sometime+todoHowlongdidittakeyoutofinishthework?③It＋be＋形容词＋forsb＋todoItisdifficultforustofinishwritingthecompositioninaquarterofanhour.④It＋be＋形容词＋ofsb＋todoItisstupidofyoutowritedowneverythingtheteachersays.⑤Itseems(appears)＋形容词＋todoItseemedimpossibletosavemoney.在句型③中，常用表示客观情况的形容词，如：difficult,easy,hard,important,impossible,necessary等；在句型④中，常用careless,clever,good,foolish,honest,kind,lazy,nice,right,silly,stupid,wise等表示赞扬或批评的词。在不定式前的sb，可看作其逻辑主语。这一句式有时相当于Sbis＋形容词＋todo句式，如：It'skindofyoutohelpmewithmyEnglish.=YouarekindtohelpmewithmyEnglish.⒉动名词作主语Learningwithoutpracticeisnogood.动名词作主语时，也常用It句式。如：①It's+nogood(nouse,fun,apleasure,awasteoftime)+doing…It'snogoodreadingindimlight.It'snousesittingherewaiting.②It's＋形容词＋doingIt'sdangerousswimmingintheseainwindydays.这样用的形容词有expensive,nice,tiring等，但important,necessary则不适用于这种结构，应用不定式代替，如：It'simportantforyoutokeepfit.③Thereisno+doingThereisnosayingwhatwillhappennext.在这一结构中，动名词后常带宾语，相当于"It'simpossibleto…"结构。⒊动词不定式和动名词作主语的区别①不定式作主语经常表示具体动作，常与特定的动作执行者联系在一起；而动名词作主语经常表示抽象动作，经常不与特定的动作执行者联系在一起。如：It'snogoodeatingtoomuchfat.It'snogoodforyoutoeatsomuchfat.②动名词结构作主语，可以用名词或代词属格形式作逻辑主语。如：It'snouseyourpretendingthatyoudidn'tknowtherules.二、作宾语⒈不定式作宾语①以下动词后，只能跟不定式作宾语。如：agree,ask,aim,arrange,choose,decide,demand,expect,fail,help,hope,lean,long,manage,offer,plan,prepare,pretend,promise,refuse,wish等，这些词大部分可接that引导的从句。如：Idecidedtoaskformymoneyback.IdecidedthatIwouldaskformymoneyback.Whenourvisittothefarmwasover,weexpectedtostartbackonfoot.Whenourvisittothefarmwasover,weexpectedthatwewouldstartbackonfoot.②当复合宾语中的宾语是不定式时，先用形式宾语it代替不定式，把不定式置于补语之后，即：主语＋动词＋it＋补语＋todo句式。如：Wethinkitquiteimportantforustolearnaforeignlanguagewell.Hefeelsithisdutytohelpthepoor.③介词but,except,besides+todo(do)在这种句型中，如介词前有动词do，后面应接不带to的不定式；如无do，则接to不定式，即带do不带to，带to不带do。如：Theenemysoldiershadnochoicebuttogivein.OnSundayafternoonIhadnothingtodobutwatchTV.⒉动名词作宾语①以下动词后，只能接动名词作宾语，如：admit,appreciate,consider,delay,enjoy,finish,keep,imagine,mind,miss,practise,resist,risk,save,suggest,don'tmind,giveup,insist,on,putoff等。如：Isuggestspendingoursummervacationinaseasidetown.Youmustgiveupsmoking,foritdoestoomuchharmtoyourhealth.②动名词作介词的宾语Ishouldgotoattendthebirthdaycelebrationinsteadofstayingathome.WhataboutinvitingLiJuntomakeaspeech?动名词前的介词有时可以省略，如：havedifficulty(in)doing,havenotrouble(in)doing,losenotime(in)doing,prevent/stop…(from)doing,thereisnouse(in)doing等。⒊部分动词后面，既可接动词不定式，也可接动名词作宾语，意义不变。如：begin,continue,start,hate,like,love,need,require,want等。在need,require,want后接-ing形式，表...
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