選擇線上英語課程，可以讓自己掌握更多的知識，提升英語水平。今天和大家來分享的是英語語法知識當中的主語從句(Subject Clause)， 主語從句即在主從復合句中充當主語成分的句子。對此還不太了解的，今天可以一起來往下看看。

It is important.

That we all should attend the meeting is important.

It is important (that) we all should attend the meeting.

主語從句的連詞

1、連詞that(句首不可省略)，whether，if引導的主語從句。

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”，其語義不變。但如果主語從句位于句首則必須用連接詞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、連接代詞who，whose，what，which，wh ever引導的主語從句。

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、連接副詞 where，when，how，why引導的主語從句。

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：主語從句中的連詞不能重疊使用。

That whether we’ll go camping tomorrow depends on the weather. (X)

Whether we’ll go camping tomorrow depends on the weather. (√)

主語從句的語序

主語從句的語序用陳述語序

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)

主語從句的時態

主語從句的時態不受主句時態影響和限制。

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.

主語從句的注意事項

1. 主語從句的謂語一般用單數形式;

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引導的主語從句，可根據表語決定主句動詞的單復數形式;

What he needs is that book.

What he needs are some books.

3. What引導的主語從句一般不可以改為含形式主語的句子，that則可以;

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. 常見用it做形式主語的主語從句

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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