关于代词it在定语从句中的修饰问题His fortune is greater or less,precisely in proportion to the extent of this power; or to the quantity either of other men's labour,or,what is the same thing,of the produce of other men's labour,which it enables him to purchase or command.最后一句当中的it 请问是指代什么,该怎么判断?

关于代词it在定语从句中的修饰问题
His fortune is greater or less,precisely in proportion to the extent of this power; or to the quantity either of other men's labour,or,what is the same thing,of the produce of other men's labour,which it enables him to purchase or command.最后一句当中的it 请问是指代什么,该怎么判断?