问题补充：
--- Catherine, I have cleaned the room for you.
---Thanks. You it. I could manage it myself.
A. needn’t do
B. needn’t have done
C. mustn’t do
D. shouldn’t have done
答案：
A. needn’t do
(答案→)B. needn’t have done
C. mustn’t do
D. shouldn’t have done
解析：句意：凯萨琳，我已经为你打扫了房间。--谢谢，你本不必这么做，我自己能行。因为房间已经打扫过了，所以是needn’t have done本不必做而做了，A. needn’t do不必做（事实），C. mustn’t do禁止做，D. shouldn’t have done本不应该做而做了，根据句意选B。
