同位语从句常位于idea， fact， news， fear， belief， doubt， proof， evidence等名词后面，对这些名词作进一步解释。同位语从句大多由关联词that 引导(that不可以省略)。如：

The fact that the money has gone does not mean it was stolen.

Have you heard the news that we will have a picnic next week?

There can be no doubt that my brother is qualified for the job.

Where did you get the idea that the class would be cancelled?

So far there is no proof _______ spaceships from other planets do exist.

A. which B. that C. how D. what

答案 B

5.定语从句

定语从句分为限定性定语从句和非限定性定语从句。

限定性定语从句是句子不可缺少的一部分，没有它，句子不能成立，或意思不清楚，不说明问题。

非限定性定语从句只对其修饰的部分作进一步的说明，没有它句子其他部分仍然可以成立。非限定性定语从句常用逗号与前面的部分隔开。