You look so tired. You have stayed up again.A. shouldB. canC. mayD. must

问题补充：

You look so tired. You have stayed up again.

A. should

B. can

C. may

D. must

答案：

A. should

B. can

C. may

(答案→)D. must

解析：“你看起来很累。你肯定又熬夜了。”should应该， can可能，可以，may可能，可以， must必须，所以答案D。