Last Sunday we heard them sing Peking Opera in that theater.应改为They were heard to sing Peking OLast Sunday we heard them sing Peking Opera in that theater.应改为They were heard to sing Peking Opera in that theater last Sunday.为什么不可以是They were heard by singing Peking Opera in that theater last Sunday
问题描述：
Last Sunday we heard them sing Peking Opera in that theater.应改为They were heard to sing Peking O
Last Sunday we heard them sing Peking Opera in that theater.
应改为They were heard to sing Peking Opera in that theater last Sunday.
为什么不可以是They were heard by singing Peking Opera in that theater last Sunday
答
意思有差别.
be heard to do是有人听见他们做什么.
be heard by doing是有人因为什么而听见了他们.