Question

【题目】I heard Mary _______ the piano at that time.
A.play
B.played
C.playing
D.to play

Answer 1

【答案】C
【解析】hear sb do sth 听见某人做某事（指听见全过程）；hear sb doing sth 听见某人正在做某事。句末的 at that time （在那时）是过去的时间点，故选 C。句意是：那时我听见玛丽正在弹钢琴。