—How was the professor's lecture?
—Impressive. Thank you so much for giving me a lift during the rush hours. If not, I the lecture today.
A. couldn't attend
B. might not have attended
C. mustn't have attended
D. can't have attended
网友回答
A. couldn't attend
(答案→)B. might not have attended
C. mustn't have attended
D. can't have attended
解析：考察情态动词的虚拟语气。根据句意可知，该句是对过去的虚拟，故排除A。句意为如果不是你给的便车，我可能就无法参加今天的讲座了。
C意为禁止参加 D意为不可能参加。