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)。