hear sb do sth = sb be heard to do sth （變成被動(dòng)語(yǔ)態(tài)時(shí)不定式要還原）另外,hear sb doing sth = sb be heard doing sth (指動(dòng)作正在進(jìn)行）不可能是 to be playing ...根據(jù)句意‘經(jīng)常被聽(tīng)到彈鋼琴’ 不是正在進(jìn)行...我的問(wèn)題是為什么不選he was often heard to be playing the piano.我問(wèn)的不是為什么不選he was often heard playing the piano.我的問(wèn)題在于動(dòng)詞不定式后面的時(shí)態(tài)為什么不能選進(jìn)行時(shí)？固定用法：

hear sb do sth = sb be heard to do sth （變成被動(dòng)語(yǔ)態(tài)時(shí)不定式要還原）
hear sb doing sth = sb be heard doing sth

請(qǐng)記??！