before 后面是一个介词性宾语从句吗?

before 后面是一个介词性宾语从句吗?
The Greeks assumed that the structure of language had some connection with the process of thought, which took root in Europe long before people realized how diverse languages could be.1、“,”后面的which引导的是一个非限制性定语从句,主要是其后面的部分有些理解晦涩.2、问题如下：1）before后面是一个介词宾语从句吗?2）how引导的句子,是realized后面的宾语从句吗?3）动词could be 怎么理解?省略了什么?由什么丛当宾语?4）before前面的那个 long是属于副词性质吗? 3、结构图示分析如下：【which took root in Europe long （before people realized） how diverse languages could be.】 宾从 []