The doubt is who has taken away the valuable vase.

　　疑点是谁拿走了那只贵重的花瓶。

　　My topic today is what most scientists are researching.

　　我今天的话题就是大多数科学家正在研究的课题。

　　All this was over twenty years ago，but it's as if it was only yesterday.

　　虽然这是20多年前的事了，但宛如昨天发生的一样。

　　表语从句中应注意的问题：

　　1．because，why引导的表语从句。

　　That's because he didn't tell me the truth.(That's because...强调原因)

　　那是因为他没有告诉我真相。

　　That's why he got angry with me.(That's why...强调结果)

　　那正是他对我生气的原因。

　　2．what引导的主语从句表示结果或名词reason作主语时，后面的表语从句表示原因时要用that引导，不宜用because。

　　What cost him his life was that he was too careless.

　　使他丧命的原因是他太粗心了。

　　The reason why I was sad/for my being sad was that he didn't understand me.

　　我难过的原因是他不理解我。

　　3．使用虚拟语气的表语从句

　　在表示建议、劝告、命令含义的名词后的表语从句中，谓语动词需用"should＋动词原形"表示，should可省略。常见的词有：advice，suggestion，order，proposal，plan，idea，request，requirement等。

　　My suggestion is that we (should) have a discussion about this matter instead of just laying it aside.

　　我的建议是我们应当讨论一下这个问题，而不是把它放在一边。

　　as if/though引导的表语从句常置于系动词look，seem，sound，be，become等后面，常用虚拟语气，即形式常用过去式的某种时态。

　　The elephant feels as if/though it were a wall.

　　大象摸起来像一堵墙。

　　二、主语从句

在复合句中，作主语的从句叫作主语从句。