Question

You know that here is also a rule是什么从句？

Answer 1

这里连词that引导的是一个宾语从句，整个从句做及物动词that的宾语。that不做句子成分，也没有含义，可以省略。宾语从句的用法简介：

1.宾语从句接在及物动词后面，使用陈述语序。引导宾语从句的连词有that/which/who/whether/how等。

I don't know whether he Will come.

We don't decide where we will hold the event.

2. 宾语从句接在介词后面，此时的that不能省略。

I know nothing about him except that she comes from Africa.

I am listening to what the man is talking about.

3. it做形式宾语，代替that引导的真正宾语从句，主要用在及物动词make, take后面。

The family made it a rule that everyone should get up at 6 am.

Mr Green makes it clear that all should arrive at school on time.

Don't take it for granted that man was born wise.

Answer 2

know 为动词，动宾结构，因此是宾语从句