当 need, want, require, be worth后面接doing时，表示的是被动意义。例如：
Your hair wants cutting. 你的头发该理了。
The floor requires washing. 地板需要冲洗。
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 cleaned 则也为正确答案。