When the cat is away,the mouse/mice will play happily.后面用哪个名词,为什么?the cat--the mouse?

问题描述:

When the cat is away,the mouse/mice will play happily.后面用哪个名词,为什么?the cat--the mouse?
回答不清的就请免答,我这是要讲给学生听到,

the cat...the mouse...
英语中的parallel structure,平行结构,所以单数对单数, the A...the B.