If as one people speaking the same language they have begun to do this

问题描述:

If as one people speaking the same language they have begun to do this
请帮忙分析下这个句子结构

如果一个说同一种语言的民族已经开始这么做.
整个句子是个无主句,是个条件状语.they 是one people 的同位语.请问这里speak为何加ing呢speaking是动名词,作定语修饰people。如果不加ing就是动词谓语,就不是无主句了。