— Are you going to Beijing by air?— It’s fast but expensive. So I’m not sure. I take a

问题补充：

— Are you going to Beijing by air?

— It’s fast, but expensive. So I’m not sure. I take a train.

A. may

B. will

C. must

D. should

答案：

(答案→)A. may

B. will

C. must

D. should

解析：考查情态动词用法。may表示一种可能性比较小的推测，will 将，must是肯定性的推测，should应该，根据题中So I’m not sure，可知是一种不太肯定的推测，所以选A。