注意：当 need, want, require, worth(形容词)后面接doing也可以表示被动。

Your hair wants cutting.你的头发该理了。

The floor requires washing. 地板需要冲洗。

The book is worth reading.这本书值得一读。

典型例题

The library needs___, but it’ll have to wait until Sunday.

A. cleaning B. be cleaned C. clean D. being cleaned

答案A. need (实意) +n /to do，need (情态)+ do，当为被动语态时，还可need + doing. 本题考最后一种用法，选A。如有to be clean 则也为正确答案。

典：done，"不可能已经"。must not do 不可以（用于一般现在时)。