1. 可接表语从句的连系动词有be, look, seem, sound, appear等。
China is no longer what she used to be. 今日的中国不再是过去的中国了。
The question remains whether they will be able to help us.
At that time, it seemed as if I couldn't think of the right word.
2. 从属连词whether, as, as if / though引导的表语从句
He looked just as he had looked ten years before.
It sounds as if someone is knocking at the door. 听起来好像有人在敲门。
3. because, why引导的表语从句
That's because he didn't understand me.
那是因为他没有理解我。 (That's because...强调原因)
That's why he got angry with me.
那正是他对我生气的原因。 (That's why...强调结果)
The reason why I was sad was that he didn't understand me.
4. 连接代词who, whom, whose, what, which, whoever, whatever, whichever
连接副词 where, when, how, why。如：
The problem is who we can get to replace her. 问题是我们能找到谁去替换她呢。
The question is how he did it. 问题是他是如何做此事的。
That was what she did this morning on reaching the attic.
The trouble is that I have lost his address. 麻烦是我把他的地址丢了。
表示，should可省略。常见的词有：advice, suggestion, order, proposal, plan,
My suggestion is that we (should) start early tomorrow.