语法
- 句子主语由从句充当
- 主语从句要以引导词开头，这些引导词属于连接代词/连接副词
主语从句的结构
主语从句 + 句子其他成分
The fact is obvious.
包含确定信息
- That the rabbit ate a carrot is obvious.
包含不确定信息
- Whether the rabbit ate the carrot is obvious.
- Where the rabbit ate the carrot is obvious.
- When the rabbit ate the carrot is obvious.
- How the rabbit ate the carrot is obvious.
- Who ate the carrot is obvious.
- What the rabbit ate is obvious.
It + 句子其他成分 + 主语从句；It是形式主语
It is obvious whether the rabbit ate the carrot.
It is obvious where the rabbit ate the carrot.
It is obvious when the rabbit ate the carrot.
It is obvious how the rabbit ate the carrot.
It is obvious who ate the carrot.
It is obvious what the rabbit ate.