A. has begun
B. had been on
C. began
D. begins
答案B
主句的动作发生在从句的动作之前，表示“过去的过去”，故用过去完成时。
When I arrived at the office, the meeting ________ for ten minutes.
A. has begun
B. had been on
C. began
D. begins
答案B
主句的动作发生在从句的动作之前，表示“过去的过去”，故用过去完成时。
A. has begun
B. had been on
C. began
D. begins
答案B
主句的动作发生在从句的动作之前，表示“过去的过去”，故用过去完成时。