为你解答.
I heard Jane playing the piano in her room.(变被动语态)
Jane was heard playing the piano in her room.
Jane被听到正在她的房中弹琴.
解释:这道题的答案没问题.你老师说的是另一种情况,hear sb do sth,听到某人做了某事.该短语变为被动时,要补上不定式的to,即be heard to do.
但这句是hear sb doing,听见某人正在做,用的是现在分词doing,而非不定式.不要把这两个表达混在一起了.