问题补充：
---Must I clean the floor now?
---. It is too dirty.
A. Yes, you needn’t
B. No, you needn’t
C. No, you mustn’t
D. Yes, you must
答案：
A. Yes, you needn’t
B. No, you needn’t
C. No, you mustn’t
(答案→)D. Yes, you must
解析：对于must 引导一般疑问句的肯定回答为yes ，….must否定回答为no，….needn’t/don’t have to，故选D
