主语从句讲解及其练习

主语从句讲解及其练习
主语从句是一个句子，用作句子的主语。

主语从句有三种连词类型。

第一种是从属连词引导的主语从句，包括that、whether
和if。

其中，that引导主语从句时，that本身没有意义，不做
成分，不能省略。

例如：It seems unlikely that you will win the medal。

主语从句通常用it作形式主语。

而whether引导主语
从句时，whether本身有意义（表示“是否”），不能省略。

注意，不能用if引导主语从句，只能用whether。

例如：Whether we will hold a party in the open air tomorrow depends on the ___.
第二种是由连接代词引导的主语从句，包括who、whose、whom、which、what、___、whomever、whichever和whatever。

连接代词在句中起名词性作用，担当一定成分。

例如：What you need is ___ we do is to serve the people。

注意，whatever和whoever在主语从句中不含疑问意义，可以在从句中作主语、
宾语、表语等。

例如：Whoever breaks the law should be punished。

Whoever breaks the law。

he should be punished.
最后，要注意主语从句的格式和语法正确，避免明显的段落错误。

三、形式主语it的使用
有时为了句子的平衡，我们会在主语从句处使用形式主语it，将真正的主语从句放到句末。

这种情况分为四种情况：
1) 对于以连词that引导的主语从句，通常用形式主语it
替代主语从句，形式为It is + 名词 + 从句。

例如：
It is a fact that…（事实是……）
It is good news that…（是好消息）
___…（是个问题）
It is common knowledge that…（是常识）
类似的名词还有：a pity、a wonder、a good thing、no wonder、surprise等。

例如：
It is a mystery to me how it all happened.（这一切是如何发生的对我来说是个谜）
It is common knowledge that the whale is not a fish.（鲸鱼不是鱼是常识）
It is no surprise that Bob should have won the game.（___应该赢得比赛并不令人惊讶）
2) 对于以连接副词when、where、why、how引导的名词性从句，其连接副词有含义，在句中作状语。

例如：Where we should leave it is a problem.（我们应该把它放在哪里是个问题）
When they will come hasn't been made public.（他们什么时候来还没有公开）
3) 形式主语it还可以和形容词一起使用，形式为It is + 形容词 + 从句。

例如：
It is ___…（有必要……）
It is clear that…（很清楚……）
It is ___…（很可能……）
___…（重要的是……）
类似的形容词还有：strange、natural、us、true、good、wonderful、possible、unlikely、quite、unusual、certain、evident、worth-while、surprising、interesting、astonishing等。

例如：
It is doubtful whether she will be able to come.（她能否来还
是个疑问）
It is essential that he should be here by the weekend.（他周
末一定要来这里）
It is ___。

it is ___.
It should be noted that in such subject clauses。

the verb is often in the form of "should + infinitive"。

which requires the use
of the subjunctive mood.
For example。

"It is said that" means "according to what people say"。

"It is reported that" means "according to what has been reported"。

"It has been proved that" means "it has been proven"。

and "It must be proved that" means "it must be pointed out".
Other ___ "known"。

"estimated"。

"expected"。

"believed"。

"thought"。

"hoped"。

"noted"。

"discussed"。

"required"。

"decided"。

"suggested"。

"demanded"。

"made clear"。

"found out"。

etc.
For instance。

"It used to be thought that a new star ___" "It has not been made clear when the new road will open to traffic."
It seems" ___) that cannot be placed before the subject clause.
For example。

"It ___." "It ___." "It ___."
___ (adverbs)。

a formal subject can be used to replace the subject clause。

or the subject clause ___.
For example。

"Whether they would support us was a problem." means "It was a problem whether they would support us."。