He was heard three songs in the next room.A. singB. to singC. singingD. sung

问题补充：

He was heard three songs in the next room.

A. sing

B. to sing

C. singing

D. sung

答案：

A. sing

(答案→)B. to sing

C. singing

D. sung

解析：考查不定式做补足语的用法：动词hear后面接宾语+不带to的不定式，变成被动式就是be heard to do，要还原to，句意：有人听见他在隔壁房间唱了三首歌。选B。