同学你好，该知识点来自沪江网校《新概念英语第三册【随到随学班】》的课程，想要更系统的学习，欢迎进入课程学习。不仅可以和更多的同学一起学习，而且还有老师、助教随时的学习指导和知识点解答哦。

同学好：
在句子中担当主语的从句就叫做主语从句，通常放在主句谓语动词之前或由形式主语it代替，而本身放在句子末尾。

主语从句使用陈述语序，其通常结构为“引导词 + 主语 + 谓语 + 其他成分, 但当连接代词同时充当从句主语时，其结构为“连接代词 + 谓语 + 其他成分”。

引导词——
1. that引导
eg. That you are coming to London is the best news I have heard this long time.

2. whether引导
eg. Whether they would come to the conference was a question.

3. 连接代词引导: who,whom, whose, what, which, whoever, whomever, whichever, whatever
eg. Whoever is top from wins the game when two matched players meet.

4. 连接副词引导: therefore, besides, otherwise, however, moreover, still, thus, meanwhile
eg. How this happended is not clear to anyone.

5. 关系代词型what引导
eg. What really matters is that you are all right.

祝学习愉快！