—What did Mr. Smith do in the middle of the night?—Well, I’m not

—What did Mr. Smith do in the middle of the night?—Well, I’m not sure, but he was often heard _______.
A、singing the same song
B、to sing the same song
C、sing a same song
D、to be playing same song
【正确答案】：A
【题目解析】：be heard doing sth.被听见做某事