---Sorry Professor Smith. I didn’t finish the assignment yesterday.---Oh you have done i

问题补充：

---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

答案：

A. must

B. mustn’t

(答案→)C. should

D. shouldn’t

解析：本题考查的是虚拟语气。此处表示和过去事实相反的情况，应该用should + have + 过去分词。本来应该做，而未做。选C。