1、可以接表语从句的连系动词有be, look, remain, seem等，引导表语从句的词有,从属连词，that, weather, as though等，连接代词who, what, 连接副词when, where, why, how等等
2、that在引导表语从句时无词义，而weather有词义，意为是否，这时主句的主语常常是一些抽象的名词，如question, trouble, problem, result等等，表语从句对主句主语进行说明解释，使主语的内容具体化
3、例如，the trouble is that he has lost his money, 再例如，the question is whether we need more ice cream，问题是是否我们需要更多的冰淇淋
4、连接代词who, what, which, whom, whose, whatever, whoever, whomever, whichever等引导的表语从句，在句中作主语，宾语，表语，且连接代词不能省略
5、例如 ，the question is which of us should go, 再例如，the problem was who could do the work, 问题是谁可以做这项工作
6、由连词because, as if/as though等引导的表语从句，例如that's because we never thought of it, 那是因为我们从来没想过此事
