they are doing their _____(homework) in the classroom

问题描述:

they are doing their _____(homework) in the classroom

they are doing their homework__(homework) in the classroom
填原形,homework是一个不可数名词.
do one's homework 做家庭作业
这是五年级的题目,homework是所有家庭作业的统称,没有复数形式.OK?