The lady have done something wrong, because she is looking guilty.
A. would
B. should
C. can
D. must
网友回答
A. would
B. should
C. can
(答案→)D. must
解析： 句意：这个女士一定做了错事，因为她看起来很内疚。表示肯定推测用“must have done”，would have done“本来会做”，can have done“本可以做却没有做”，should have done过去本应该做却没有，所以选D。