注意：當 need, want, require, worth(形容詞)後面接doing也可以表示被動。
your hair wants cutting. 你的頭髮該理了。
the floor requires washing. 地板需要衝洗。
the book is worth reading. 這本書值得一讀。
典型例題
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 (實意) +n /to do，need (情態)+ do，當為被動語態時，還可need + doing. 本題考最後一種用法，選a。如有to be clean 則也為正確答案。
典：done，"不可能已經"。must not do 不可以（用於一般現在時)。