Doris' success lies in the fact that she is cooper

问题补充：

Doris success lies in the fact that she is cooperative and eager to learn from others为什么添 that

答案：

that后面的部分全部是对fact所指具体内容的解释,这个就是所谓的同位语,语法规定引导词必须用that

======以下答案可供参考======

供参考答案1:

同位语从句 that作为连接词不能省