---Sorry, Professor Smith. I didn't finish the assignment yesterday.
---Oh, you have done it as yesterday was the deadline.
A. must
B. mustn't
C. should
D. shouldn't
网友回答
A. must
B. mustn't
(答案→)C. should
D. shouldn't
解析：句意：--对不起，史密斯教授，我昨天没有完成作业。--哦，你应该早完成它，因为昨天是最后期限。should have done指过去应该做的还未做，故选C。