选择线上英语课程，可以让自己掌握更多的知识，提升英语水平。今天和大家来分享的是英语语法知识当中的主语从句(Subject Clause)， 主语从句即在主从复合句中充当主语成分的句子。对此还不太了解的，今天可以一起来往下看看。
It is important.
That we all should attend the meeting is important.
It is important (that) we all should attend the meeting.
主语从句的连词
1、连词that(句首不可省略)，whether，if引导的主语从句。
That the earth is round is true.
It is true that the earth is round.
That you missed such an interesting film is a pity.
It is a pity that you missed such an interesting film.
That she is still alive is sheer luck.
It is sheer luch that she is still alive.
It remains unknown whether/if we will go for an outing tomorrow.
注意：whether/if含有“是否”的意思，可以加上“or not”，其语义不变。但如果主语从句位于句首则必须用连接词whether，不用if。
If the meeting will be put off hasn't been decided yet. (X)
Whether the meeting will be put off hasn't been decided yet. (√)
It is still a question whether/if it is true or not.
Whether it is true or not is still a question.
2、连接代词who，whose，what，which，wh+ever引导的主语从句。
Who will come to teach the students is not known.
Whom the watch belongs to is unknown.
Whose watch was lost is unknown.
Whatever he said wasn't true.
3、连接副词 where，when，how，why引导的主语从句。
Where the library is to be built has not been decided yet.
When we start the work is an important question.
How this happened is not clear.
Why she was late for school is quite clear now.
注意：主语从句中的连词不能重叠使用。
That whether we'll go camping tomorrow depends on the weather. (X)
Whether we'll go camping tomorrow depends on the weather. (√)
主语从句的语序
主语从句的语序用陈述语序
When will she come is not known.(X)
When she will come is not known. (√)
What we need is more time. (√)
What do we need is more time.(X)
主语从句的时态
主语从句的时态不受主句时态影响和限制。
What caused the accident remains unknown.
What he did yesterday will never be known by his mother.
It is certain that he will win the match.
It is suggested that the work should be done with great care.
主语从句的注意事项
1. 主语从句的谓语一般用单数形式;
When the meeting will be held haven't been known yet.(X)
When the meeting will be held hasn't been known yet. (√)
When he will come is a puzzle. (√)
2. What引导的主语从句，可根据表语决定主句动词的单复数形式;
What he needs is that book.
What he needs are some books.
3. What引导的主语从句一般不可以改为含形式主语的句子，that则可以;
What you said yesterday is right.
It is right what you said yesterday.(X)
That she is still alive is certain.
It is certain that she is still alive. (√)
4. 常见用it做形式主语的主语从句
It is known to all that the gunpowder was first invented by the Chinese.
It is true that he has made a very important discovery in chemistry.
It is important that we all should attend the meeting.
It is a pity that we won't be able to go to the south to spend our summer vacation.
It is doubtful whether she will be able to come.
It is said that he has gone to Shanghai.
It is still a mystery what caused the accident.
It seems obvious that we can not go on like this.
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