1.表语从句:就是用一个句子作为表语。说明主语是什么或者怎么样，由名词、形容词或相当于名词或形容词的词或短语充当，和连系动词一起构成谓语。
Eg:The problem is puzzling.这问题令人困惑
主语 连系动词 形容词作表语
The problem is when we can get a pay rise.问题是什么时候我们可以得到加薪.
主语 连系动词 一个句子作表语---表语从句
2.连接表语从句的连接词有：that, what, who, when, where, which, why, whether,how.
He has become a teacher.他已经成为一名教师。
He has become what he wanted to be ten years ago.
他已经成为了他10年前想成为的。
She has remained there for an hour.
她曾在那里停留了一个小时。
She has remained where I stood yesterday for an hour.
她一直在我昨天站的地方站了一个小时。
His suggestion is good.他的建议是好的。
His suggestion is that we should stay calm.
他的建议是，我们应该保持冷静。
The question is when he can arrive at the hotel.
问题是，他什么时候可以到达酒店。
who will travel with me to Beijing tomorrow.
谁与我明天将前往北京。
why he cried yesterday.昨天他为什么哭。
how I can persuade her to join us in the party.
我怎么能说服她加入我们的派对。
whether the enemy is marching towards us.
是否敌人正向我们行进.
