名词性从句在句中起名词作用，可作主语、宾语、表语、同位语。
常见引导词：
that
whether/if
what, who, whom, whose, which
when, where, why, how14.1 主语从句
What he said is true.
他说的话是真的。
That he passed the exam surprised us.
他通过考试让我们惊讶。为了避免主语过长，常用 it 作形式主语：
It surprised us that he passed the exam.
他通过考试让我们惊讶。14.2 宾语从句
I know that he is honest.
我知道他很诚实。
She asked whether I needed help.
她问我是否需要帮助。
Do you know where he lives?
你知道他住在哪里吗？注意宾语从句要用陈述语序：
错误：Do you know where does he live?
正确：Do you know where he lives?14.3 表语从句
The problem is that we don't have enough time.
问题是我们没有足够的时间。
This is what I want.
这就是我想要的。14.4 同位语从句
同位语从句解释说明前面的抽象名词。
常见抽象名词：
fact, news, idea, belief, hope, doubt, question, possibility例句：
The news that he won the game excited us.
他赢得比赛的消息让我们兴奋。
I have no doubt that she will succeed.
我毫不怀疑她会成功。14.5 that 和 what 的区别
that 在名词性从句中通常不作成分，只起连接作用。
I know that he is right.
我知道他是对的。what 在从句中要充当成分，意思相当于“……的东西/事情”。
I don't understand what he said.
我不理解他说的话。what 作 said 的宾语。