问题补充：
My sister met him at the Grand Theatre yesterday afternoon，so he your lecture.
A. couldn have attended
B. needn have attended
C. mustn have attended
D. shouldn have attended
答案：
(答案→)A. couldn have attended
B. needn have attended
C. mustn have attended
D. shouldn have attended
解析：
“情态动词＋完成式”有各自的含义。must have done表示对过去事情的肯定推测，多用于肯定句中；needn have done表示过去本不必做的事情；shouldn have done表示过去做了不该做的事情；can (couldn )have done表示对过去的否定性推测，意为“不可能”。所提供的情境My sister met him at the Grand表示他不可能参加讲座。
