school,sister,mother,father,parent,brother,grandmother,grandfather,grandpareng,family,day复数形式
问题描述：
school,sister,mother,father,parent,brother,grandmother,grandfather,grandpareng,family,day复数形式
答
school,sister,parent,brother,grandparent,day都是直接加s
family变为families
其他的几个没有复数，因为是唯一的。
原则上mother,father,grandmother,grandfather是没有复数的。但是还要看具体语境。有时要在后面加上s。如
The students' fathers are on the way to the school.
答
schools,sisters,parents,brothers,famiies
答
除了,family要改成families外,其他的直接加s就行了
答
schools,sisters,mothers,fathers,parents,brothers,grandmothers,grandfathers,grandparents,families,days