问题补充：
My sister met him at the street yesterday afternoon, so he your lecture.
A. shouldn’t have attended
B. couldn’t have attended
C. mustn’t have attended
D. needn’t have attended
答案：
A. shouldn’t have attended
(答案→)B. couldn’t have attended
C. mustn’t have attended
D. needn’t have attended
解析：考查情态动词用法。Shouldn’t have done本不应该做某事，实际上却做了（虚拟语气）；couldn’t have done不可能做某事（对过去情况的推测）；needn’t have done本不需要做某事，实际上却做了（虚拟语气）；句意：我的姐姐昨天下午在街上遇见了他，所以他不可能去听了你的演讲。故B正确。
