The ambulance controller told him an ambulance _ in five minutes.

A. were arriving 过去进行时态

B. would be arriving 过去将来进行时态

C.  will be arriving 一般将来进行时态

D.would have arrived 过去将来完成时

答案解析B,因为主句为过去时态，其宾语从句也应该为过去某种时态，根据动作属于将要发生，应该用过去将来进行时态。