That day I saw some parents (sit)at the back of the classroom ,(listen)to the teacher.用适当形式

问题描述:

That day I saw some parents (sit)at the back of the classroom ,(listen)to the teacher.用适当形式

sitting,listening
see sb doing 强调看到某人正在做某事
根据题意应该是看到家长正在听老师讲话