主語從句
用作主語的從句叫主語從句。
(That the earth goes around the sun) is known to all.
(How this happened) is not clear to anyone.
(Whoever comes) is welcome.
(When we shall have our sports meeting) is still a question.
(Whether he will come today) is still unknown.
注意：
1. 主語從句是特殊疑問句，應該用特殊疑問詞加陳述句語序。
2. that引導的主語從句放在句首，不可省略that。
3. 主語從句常用it作形式主語，真正的主語放在后面，這時that可省略。
It's a pity (that) you missed such a good opportunity.
It's still a question when we shall buy the new equipment.
It's still unknown whether he will come or not.
4. It is + P.P.+ that ; It + Vi + that，It作形式主語。
It is said that the president will visit our company.
It seems that he has caught a cold.