英语语法

1.主语从句：That the earth goes around the sun is known to us all.

2.宾语从句:The teacher said that the earth goes around the sun.

3.表语从句:One of the greatest discoveries was that the earth goes around the sun.

4.同位语从句：The fact that the earth goes around the sun is known to us all.

that做从属连词还是关系代词还是关系连词（副词）？