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)。