that在这个句子中的作用

that 是主句experts say的宾语从句标志,通过and连接与Kim Jong-Um is in the process of consolidating power并列.那为什么不能省略呢?因为宾语从句有规定：and连接两个宾语从句,that宾语从句放在and的后面时,that不能省略.另外that不能省略的情况还有：I know nothing about him except that he is from the south.(that引导的宾语从句作介词宾语时,that不能省略.)
对他我一无所知,只知道他是南方人.
That he ever said such a thing I simply don’t believe.(that从句位于句首时,that不可省略.)
我简直不相信他曾说过这样的话.
We decided,in view of his special circumstances,that we would admit him for a probationary period.(主句谓语动词与that从句之间有插入语,that不可省略.)
都是我自己整理的,