问题补充：
My sister met him at the cinema yesterday afternoon, so heyour 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：考查情态动词表示推测。“情态动词+动词原形”表示对现在情况的推测；“情态动词+have done”表示对过去情况的推测；根据前半句话说明是对过去情况的推测。句意：我姐姐昨天下午在电影院里遇见了他，所以他不可能去听你的演讲的。故A正确。needn’t have attended本不必做某事，实际上却做了；shouldn’t have attended本不应该做某事，实际上却做了；这两个都表示的是虚拟语气。
