非谓语动词在句中充当除谓语以外的句子成分的动词形式叫做非谓语动词。非谓语动词分为三种形式：不定式、动名词和分词（分词包括现在分词和过去分词）不定式一、不定式的作用1、 作主语 不定式作主语时，谓语用单数。往往用 it 作形式主语，把不定式放在谓语后面。如：It took us two hours to finish the job.It is impossible for us to get there on time.It is very kind of you to help us.注意：（1）其他系动词如 look, appear 等也可用于此句型。 （2）当不定式作主语的句子中又有一个不定式作表语时，不能用 It is …to…的句型。试比较： It is to believe to see.（错） To see is to believe.（对）“百闻不如一见” （3）It is+ adj. of / for sb. to do sth. 结构中，当不定式的逻辑主语和前面的形容词可以构成系表结构时，用 of, 否则用 for.2、 作宾语（1）动词+不定式。如：He managed to escape from the fire.I find it hard to get along with him.（it 作形式宾语）（2）动词+疑问词+to , “特殊疑问句+不定式”相当于名词，作宾语。如：I don’t know what to do next/ how to do it next.I can’t make up my mind which to buy.注意：不定式短语作宾语时，如果还带有宾语补足语，往往把不定式短语放在宾语补足语之后，用 it 作形式宾语。如：I find it necessary to learn a foreign language.3、 作宾语补足语（1）动词+宾语+不定式（to do ）。如：He warned me to be careful.I want you to speak to Tom.What makes you think so?（不带 to 的不定式）（2）动词+宾语+ to be 的不定式结构。如：We consider Tom to be one of the best students in our class.The book is believed to be uninteresting.（被动语态）例子：Charles Babbage is generally considered ______ the first computer.A to invent B inventing C to have invented D having invented答案：A（3）There +不定式。如：We didn’t expect there to be so many people there.我们没料到会有那么多人在那里。注意：（1）有些动词需用 as 短语作补语，像 regard, think, believe, take, consider。如：We regard Tom as our best teacher. 我...
