— Listen! Someone is singing in the music room. It ______ be Jim. He practices singing there every day.

— It ______ be him. He has gone to Beijing. [ ]

A. can; can't

B. must; may not

C. must; can't

D. may; may not

横担定位在电杆上部，用来（）。

A、支持绝缘子

B、支持导线

C、使导线间满足规定的距离

D、水泥横担