表语从句
表语从句在复合句中作表语的名词性从句，放在系动词之后，一般结构是“主语+连系动词+表语从句”。可以接表语从句的连系动词有be, look, remain, seem等。引导表语从句的that常可省略。另外，常用的还有the reason is that… 和It is because 等结构。例如：
1) The question is whether we can make good preparation in such a short time.
2) This is why we can’t get the support of the people.
3) But the fact remains that we are behind the other classes.
4) The reason he is late for school is that he missed the early bus.
同位语从句
同位语从句就是在复合句中作名词的同位语的名词性从句。
1. 同位语从句的功能
同位语从句对于名词进一步解释，说明名词的具体内容，一般由that引导，例如：
1) The king’s decision that the prisoner would be set free surprised all the people.
2) The order that all the soldiers should stay still is given by the general.
2. 同位语在句子中的位置
同位语从句有时可以不紧跟在它所说明的名词后面，而是被别的词隔开。例如：
He got the news from Mary that the sports meeting was put off.
3. 同位语从句与定语从句的区别
(1) 定语从句中的that既代替先行词，同时以在从句中作某个成分(主语或宾语)，而同位语从句中的that是连词，只起连接主句与从句的作用，不充当句中任何成分。
(2) 定语从句是形容词性的，其功能是修饰先行词，对先行词加以限定，描述定的性质或特征;同位语从句是名词性的，其功能是对名词进行补充说明。例如：
1) The news that he told me is that Tom would go abroad next year.(他告诉我的消息是汤姆明年将出国。)(第一个that引导的从句是定语从句，that在从句中作宾语)
2)The news that Tom would go abroad is told by him.(汤姆将出国的消息是他讲的。)(同位语从句，that在句中不作任何成分)
