-- There is a lot of smoke coming out of the teaching-building there.-Really? It b

问题补充：

---- There is a lot of smoke coming out of the teaching-building there.

---- Really? It be a fire, most probably.

A. can

B. ought to

C. have to

D. must

答案：

A. can

B. ought to

C. have to

(答案→)D. must

解析：从most probably.可以看出是很可能, must表示一定