问题补充：
--- Where are the students ? How could they keep us waiting for so long?
--- They started an hour ago and they be here in fifteen 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：should在这里表示预期，“应该会，可能”。can表示有能力做或能够发生；would表示想象中的结果；must表推测，或表必须。
