简单理解：
句子只有一个主谓结构（不管这个主语有多少个，谓语有多少个）就叫做
简单句。
如：
My father and my mother are teachers and love their work.两个并列主语，两个并列谓语。但只是一个主谓结构。简单句
My father and my mother are teachers and they love their work.
两个主语My father and my mother，they；两个谓语：are teachers；love their work
两个主谓结构。
并列句。