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.
She has remained there for an hour.
She has remained where I stood yesterday for an hour.
His suggestion is good.他的建议是好的。
His suggestion is that we should stay calm.
The question is when he can arrive at the hotel.
who will travel with me to Beijing tomorrow.
why he cried yesterday.昨天他为什么哭。
how I can persuade her to join us in the party.
whether the enemy is marching towards us.
1.The question is ________ we will have our sports meet next week.
A.that B.if C.when D.whether
2.The reason why he failed is ________he was too careless.
A.because B.that C.for D.because of
3.Go and get your coat.It’ s ________you left it
A.where B.there C.there where D.where there
4.The problem is _________to take the place of Ted
A.who can we get B.what we can get
C.who we can get D.that we can get
5.What I want to know is ______ he likes the gift given by us.
A.that B.if C.whether D.不填
6.The reason is_________I missed the bus.
A.that B.when C.why D.what
7.That is __ ___ we were late last time.
A.that B.when C.why D.what
8.She looked _________ she were ten years younger.
A.that B.like C.as D.as though
9.—I fell sick!
--I think it is _______ you are doing too much.
A.why B.when C.what D.because
10.The reason why he hasn’t come is ___________.
A.because his mother is ill B.because of his mother’s being ill
C.that his mother is ill D.for his mother is ill
11.—He was born here.
-- That is _______ he likes the place so much.
A.that B.what C.why D.how
12.That is ______ Lu Xun once lived.
A.what B.where C.that D.why
1._______your father wants to know is________ getting on with your studies.
A.What; how are you B.That;how you are
C.How;that you are D.What;how you are
2.The trouble is__________we are short of tools.
A.what B.that C.how D.why that
3.America was __________was first called “India” by Columbus.
A.what B.where C.the place D.there where
4.China is becoming stronger and stronger.It is no longer_________ .
A.what it used to be B.what it was used to being
C.what it used to being D.what it was used to be
5.________he really means is ________he disagrees with us.
A.What … that B.That … what
C.What … what D.That … what
6.The energy is ________ makes the cells able to do their work.
A.that B.which C.what D.such
1 —I drove to Zhuhai for the air show last week .
—Is that_____ you had a few days off?
A.why B .what C.when D.where
2 .I had neither a raincoat nor an umbrella ____I got wet through.
A.It’s the reason B.That’s why C.There’s why D.It’s how
3.See the flags on top of the building? That was ______ we did this morning.
A.when B.which C.where D.what
4.--- Are you still thinking about yesterday’s game?
---Oh, that’s _____.
A.what makes me feel excited B.whatever I feel excited about
C.how I feel about it D.when I feel excited
5.What surprised me was not what he said but ______ he said it.
A.the way B.in the way that C.in the way D.the way which
False: The question is when can he arrive at the hotel.
Right: The question is when he can arrive at the hotel.
2.不可以用if，而用whether 连接表语从句(as if例外)。
引导宾语从句时可以互换if/whether 位于介词后要用whether，位于句首时要用whether 引导表语从句，主语从句，同位语从句时要用whether
False: The question is if the enemy is marching towards us.
Right: The question is whether the enemy is marching towards us.
Right: It looked as if he had understood this question.
Right: The question is who will travel with me to Beijing tomorrow.
Right: The question is why he cried yesterday.
例如：The problem is how we can get the things we need.(how 在表语从句中充当方式状语)
The scissors are not what I need.(what 在表语从句中充当宾语)
What I told him was that I would find him a good play.
That is what I want to tell you.(what在表语从句中充当直接宾语)
That is why she failed to pass the exam.(why在表语从句中充当原因状语)
注意：“That is why...”是常用句型， 意为“这就是……的原因/因此……”， 其中why引导的名词性从句在句中作表语， 该句型通常用于针对前面已经说明过的原因进行总结，又如： That is why you see this old woman before you know, Jeanne.(前文提到Jeanne对老妇人显得苍老憔悴深感诧异， 说话人对她讲述了其中的原因之后，用这一句来进行概括)。
That is why I came.这就是我来的原因。
③连接词:当从句意思完整,主句意思肯定时,连接词用that,且可以省去,当从句意思完整,主句意思不确定或含否定含意时, 常用if或whether(是否), 当从句意思不完整时, 连接词则是代替不完整部分的特殊疑问词。