The fog is so thick that the express way have been closedYou are right. I have

问题补充：

--- The fog is so thick that the express way have been closed.

--- You are right. I have thought of that. Now we have to take another road.

A. can; should

B. may; can

C. should; must

D. must; should

答案：

A. can; should

B. may; can

C. should; must

(答案→)D. must; should

解析：考查情态动词：第一空填must表示猜测：一定是，第二空填should have done“本该做…却没做“，句意是：--这场雾很大，高速公路一定关了。--你是对的，--我本该想到的，现在只好另外走一条路了。选D。