They find that flowing water passing away never returns，be they babbling streams or grand rivers.

划线部分为让步状语从句。这是古体形式，在现代英语中用于正式书面语。其中be为动词原型式虚拟语气（有的语法书称为现在式虚拟语气，有的叫be式虚拟语气）。省略了连词whether，虚拟语气动词倒装至主语之前。如果不倒装，则为 whether they be babbling streams or grand rivers. 注意此时be仍然是虚拟语气形式。这种虚拟语气形式在现代英语常用情态动词结构may do代替，所以等于whether they may be babbling streams or grand rivers. 现代英语非正式语体则直接用陈述语气：whether they are babbling streams or grand rivers.

下面看一个汉译英句子：

国家无论大小都享有平等都权利。

Each country, be it big or small, enjoys the equal rights. 古体，非常正式

Each country, whethe it be big or small, enjoys the equal rights. 正式语体

Each country, whether it may be big or small, enjoys the equal rights. 较为正式

Each country, whether it is big or small, enjoys the equal rights. 非正式语体