Question

that在从句中可以做主语吗？

that在从句中可以做主语吗？
在不同的从句中请分别说!

Answer 1

问题有几个不妥：
1.
宾语从句没有先行词；
2.
that是引导词不是先行词
3.
宾语从句中的that是连词，是不能充当句子成分的。只是起连接作用的。
如：
he
said
that
he
would
come
back
soon.
问题要是换成：
定语从句中引导词that可以在从句中做主语吗？
答：可以
因为定语从句是关系代词，所以，它是必须在从句中做成分的：可以做主语、宾语的。

Answer 2

定语从句：It is the knife that made you out of trouble.
主语从句：Whether that is possible does not have any needs to be judged by the manager.
宾语从句：I think that is a good idea.
表语从句：The problem is what that costs.
同位语从句：The question whether that is a UFO has just been discussed.
补足语从句：I do not know whether that is dirty, but I made the city where that is everywhere.（注意后半句才含有宾语补足语从句）
状语从句：If that is nice, I will introduce that to my friend.

但只有定语从句中的that才可能既做主语，又是引导词。

Answer 3

可以
it is the knife that help you out of trouble

Answer 4

可以
如 he asked me if that is possible.

Answer 5

why not?