need to do sth和need do sth 有什么不一样
1个回答

need可以作情态动词也可以作普通动词.

当它是情态动词的时候,肯定形式就是need do sth.否定形式是needn't do sth.

当它是普通动词时候,肯定形式是need to do sth.否定形式是don't need to do sth.

重要的是,need当情态动词时,一般不用于肯定句,且作为must提问的否定回答,如:

must I do the homework

no,you needn't.