The phone had been ringing for three minutes before it.A. answeredB. had answeredC. was an

问题补充：

The phone had been ringing for three minutes before it.

A. answered

B. had answered

C. was answering

D. was answered

答案：

A. answered

B. had answered

C. was answering

(答案→)D. was answered

解析：由主句的had been ringing判断，从句用过去时态，我们看出answer与it是被动关系。