不定式或不定式短語的用法：

不定式在句子中可作主語、表語、賓語、定語、狀語和補足語。

1．作主語

不定式或不定式短語作主語時，謂語動詞用第三人稱單數。如：

To serve the people well is our duty.

To get there on foot will take several hours.

動詞不定式短語作主語時，往往放在謂語動詞的后面，用引導詞it作形式主語。上述兩句也可改為：

It is our duty to serve the people well.

It will take several hours to get there on foot.

(take – need需要(多少時間等))

類似這樣不定式做主語的句型:

It is + n.+ to do

It a\takes sb.+ some time + to do

It is +adj.+ for sb.+ to do

It is +adj.+ of sb.+ to do

It is our duty to help them.

It will take you quite a long time to finish it.

(finish - fulfill完成)

It is easy for us to answer this question.

It is kind of you to help me

(help –aid 幫助)