问题补充：
My sister met him at the Grand Theater yesterday afternoon, so he your lecture.
A. couldn’t have attended
B. needn’t have attended
C. mustn’t have attended
D. shouldn’t have attended
答案：
(答案→)A. couldn’t have attended
B. needn’t have attended
C. mustn’t have attended
D. shouldn’t have attended
解析：考察情态动词，couldn’t have attended不可能做了某事 needn’t have attended本不需要干某事
mustn’t have attended禁止干某事 shouldn’t have attended本不应当干某事
句意为，我的姐姐昨天下午在大剧院遇到了他，因此他不可能参加了你的讲座
