---- I can’t get through to the general manager’s office anyhow.
---- The line is busy. Someone the telephone.
A. can have used
B. can use
C. must have used
D. must be using
网友回答
A. can have used
B. can use
C. must have used
(答案→)D. must be using
解析：考查情态动词推测的用法。A项中 can have used可能已经用了； B项中can use可以用；C项中must have used一定已经使用；D项中 must be using一定正在使用。句意：－我无论如何也无法打通总经理办公室的电话。-热线。一定有人在用电话。