主语从句的结构和用法？
It is (high) time that表示“是该做．．....的时候了。这种句式常用it作形式主语，that从句为主语从句，句中常用一般过去式或“should+do”的虚拟语气结构。注意：其中should不可省略，time前不加定冠词the。
结构：It's high time that sb did/should do sth
例如：It's high/good/about that we struggled/should struggle for our dream. 是时候为梦想拼搏奋斗了。
主语从句结构及用法
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
例如：That you are coming to London is the best news I have heard this long time.
2、whether引导
例如：Whether they would come to conference was a question.
3、连接代词引导： who，whom，whose，what，which，whoever，whomever，whichever， whatever。
例如：Whoever is top from wins the game when two matched players meet.
4、连接副词引导： therefore，besides，otherwise，however，moreover，stil，thus， meanwhile。
例如：How this happended is not clear to anyone.
5、关系代词型what引导
例如：What shoked me was that she never wash her own clothes.
