When I entered the step-classroom (阶梯教室), the lecture and the audience attentively.
A. began, listened
B. was begun, was listening
C. had begun, listened
D. had begun, were listening
网友回答
A. began, listened
B. was begun, was listening
C. had begun, listened
(答案→)D. had begun, were listening
解析：考查时态，句意：当我进入阶梯教室的时候，讲座已经开始了，观众正专心的听。第一空填过去完成时，表示讲座是在我进入前就开始了，第二空填过去进行时，表示我进去的时候观众正认真的听。选D。