I don't think it advisable that为什么不加is与It is advisable that句型的区别

I don't think it advisable that为什么不加is与It is advisable that句型的区别
I don't think it advisable that为什么不加is
与It is advisable that句型的区别

I don't think it advisable that为什么不加is与It is advisable that句型的区别
主语+谓语+IT+ + that从句,这是个常规结构,it作形式宾语,形容词/名词作宾语补足语,that从句是真正的宾语.
It is 形容词/名词+ that从句,It 是形式主语,从句是真正的主语（从句）.