It's not who you are underneath...but what you do

问题补充：

Its not who you are underneath...but what you do that defines you 这里面的that能去掉吗?

答案：

这个复合句中,it is是形式主语,两个what后面那串并列做表语,that引导的主语从句才是句子真正主语.所以that不可省略