可以是主语从句，宾语从句，定语从句等
如:
It （形式主语）is （系动词）sheer luck（表语） that（主语从句连接词） the miners are still alive after 10 days（真正主语）
that引导从句的用法:
1、 I know that you can speak English well.
that引导是宾语从句（that从句位于动词know之后）。that不作任何成分。
that在宾语从句中是不充当成分的。
区别： I know what you say. 我知道你说的话。
2、 I have an English book that my father bought.
that引导的是定语从句，在定语从句中充当宾语。
3、 I have a good friend that can speak Japanese.
that引导的是定语从句，在定语从句中充当主语。
4、That he will come to our school next week is sure.
that引导的是主语从句，在引导主语从句中，that是不充当成分的，无意义。后面跟的是一个完整的句子。
5、The news that he passed the English made us happy.
that引导的是同位语从句，来解释这个news（消息）。that在同位语从句中是不充当成分的。
切记：that如果是引导同位语从句，that后面必须是一个完整的句子，that本身不做成分。
注意：不一定有news，就一定是同位语从句。
比如:
6、The news that you said made us happy.
在这里，that引导的是定语从句，在定语从句中充当宾语。因为said是及物动词，后面缺少宾语
luck后的that从句是什么成分
充当宾语成分，例如：
1、It was a stroke of luck that I found you here.我在这儿看见你纯属巧遇。
2、One customer who gave the company one star wrote: "Called to get a ride and was told， 'vaccinated people aren't allowed in our cars.' Good luck with that business model."一位给该公司一颗星的顾客写道：“打电话叫车，却被告知‘接种疫苗的人禁止乘车。’祝你在这种商业模式下好运。”
3、It was only by good luck that I found such a good job.我只是幸运地找到这么好的工作。
