名词性从句和定语从句的区别

名词性从句包括：主语从句、宾语从句、表语从句和同位语从句，多由连词that，wh-疑问词或由what，whatever等关系代词引导。

1.主语从句

1)主语从句在句子中充当主语，句子的谓语动词用第三人称单数。如：

What is happening outside does not concern us.外面发生的事与我们无关。

2)主语从句前的that不能省略，仅起连接作用，有时为了保持句子平衡，that从句后置，而由it作形式主语。如：

It is estimated that a round-trip to Mars would take more than a year.据估计，飞到火星来回的时间要超过一年。

2.宾语从句在句子中充当宾语。如：

I don't know where the sound came from.我不知道声音是从哪里来的。

Don't be satisfied with what you have achieved.不要满足于你已取得的成绩。

3.当从句放在系动词be，look，remain，seem等后，即构成表语从句。如：

The trouble is that I have lost his address.麻烦的是我弄丢了他的地址。

It seems that as if it is going to snow.看起来天要下雪了。

4.同位语从句

1)同位语从句是对与之同位的名词中心词作进一步解释。能接同位语从句的常见名词有：idea, fact, news, belief, hope, evidence, opinion, problem, truth, answer, proposal, theory, decision, discovery, problem, thought, certainty, likelihood, on cond