— Lily is a happy girl, but today she seems in a bad mood.
— Something to her.
A. must happen
B. should have happened
C. could have happened
D. must have happened
网友回答
A. must happen
B. should have happened
C. could have happened
(答案→)D. must have happened
解析：根据句意应该是Lily过去肯定发生了一些事，should have happened过去本应该做某事 could have happened过去可能做了某事，must have happened过去肯定做了某事，所以答案D。