-- I can’t get through to the general manager’s office anyhow. -- The line is bu

  —— I can’t get through to the general manager’s office anyhow.

—— The line is busy. Someone＿＿＿＿＿the telephone.

A. must use     B. uses  C. must have been using     D. must be using

试题答案

D

解析:

must be using表示此刻“一定正在使用……”。