— How could they keep us waiting for so long? — They got on the bus half an hour ago and t

问题补充：

— How could they keep us waiting for so long?

— They got on the bus half an hour ago and they be here in ten minutes, I think.

A. might

B. would

C. should

D. must

答案：

A. might

B. would

(答案→)C. should

D. must

解析：考查情态动词。句中should表示“应当”之意：——他们怎么能让我们等这么久呢？——他们半个小时前上公共汽车，我想他们应当10分钟内到达这里。