表语从句在高考中出现的次数很少，而出现往往又与系动词紧密联系，因此熟练掌握连系动词很重要。 虽说不是高考的热点，但我们不能掉以轻心。下面我们连系高考试题进行分析与预测： 
一、表语从句位于系动词之后，引导表语从句的有：that, what, how, where, when, why, because, as if等，要掌握好表语从句，我们在学习中必须要注意下面要点：
1.表语从句要用陈述语序。如：
That is where the famous scientist was born.
This is why she is so happy today.
2.that和what在引导表语从句时，作用和意义都不相同。That本身没有词义，在句中只起连接作用，不充当句子成分；what则表示“所……的（人或事）”，在表语从句中充当主语或宾语等。如：
That fact is that more than seventy percent of the earth’s surface is covered by water.
What he told you was what had been discussed at the meeting.
3.If 与whether均意为“是否”，但引导表语从句时，只能用whether, 不能用if。如：
The question is whether we can finish our work by tomorrow evening.
4.As, if, though引导的表语从句 时，从句谓语多用虚拟语气。这是因为从句中的情况与事实不相符。具体来说，如果从句表示与现在事实相反，谓语动词用一般过去式；如果从句表示与过去事实相反时，谓语动词要用“had +过去分词”，如果从句表示将来的可能性不大，用would (might ,could )+动词原形，如：
Li Lei is now in a new jacket he looks as if he were an American boy.
The girl is giving us a vivid description of moon. It seems as if she had been to the moon many times.
It looks as if it might rain.
但是，如果as if ,as though 引导的表语从句所表示的与事实相符，从句则用陈述语气，如：
The clouds are gathering. It looks as if is going to rain.
二、系动词的分类
系动词有表示状态的；有表示状态变化的。
表示状态的有：
1） be, seem ,appear 等。
2） look ,sound ,feel ,taste ,smell 等，由感官动词变化而来。意思为“看（听、摸、尝、闻）起来”。
Mr. Li looks quite young. 李先生看起来很年轻。
3） stand ,keep ,prove ,remain 等由不及物动词转化而来。
The machine has been standing idle. 这台机器一直闲着不用。
2.表示状态变化的：
Become ,get ,grow, fall, turn等
He has fallen ill. 他已经病倒了。
The water ____cool when I jumped into the pool for morning exercise  (2006全国卷一)
A. was felt  B. is felt  C. felt  D. feels
分析: C feel是系动词,用主动形式表示被动意义.
三、表语从句和主语从句，宾语从句，同位语从句的相同点和不同点
相同点：
1.相同的关连词
1） 连词
2） 连接代词
3） 连接副词
2.从句均不能用逗号和主句隔开；用陈述语序。

不同点：
1.连词as if（好象，仿佛）引导表语从句（if不能引导表语从句）。能跟表语从句的谓语动词一般为系动词be, seem, look等，例如：
It looked as if it was going to rain.
2.连词because引导表语从句。例如：
I think it is because you are doing too much.
My anger is because he hadn’t written to me for a long time.
1.-I drive to Zhuhai for the air show last week.
-Is that __you had a few days off? (NMET1999)
A.why  B. when  C. what  D where
分析：选A  Why引导的表语从句中，why做原因状语。
2. The question is ____it is worth visiting.
  A. if  B. as if  C. whether  D. how
分析：选C  whether引导表语从句
3. This is _____it happened.
  A. what  B. when  C. that  D. how
分析：选D  how引导表语从句，说明事情的发生经过。
4. This is ____ the city lies.
  A. which  B. what  C. where  D. when
分析：选C  where引导表语从句，表示城市所处的位置。
5. He was ill .That is ____he didn’t come yesterday.
A. when  B. why  C. how  D. that
分析：B  because引导表语从句，表示原因。
6. That was ___ I was thirteen I entered the No.1 Middle School.
  A. because  B. why  C. how  D when
分析：选A  because引导表语从句，表原因。

高考预测：
1.The problem is ____we can master modern science and technology in a short time.
A. if  B. that  C. what  D. how
2. –Doesn’t Mr. Smith live on this street?
  -No .This is ____Mr. Brown lives.
A. which B. where C. how D. that
3. The reason why he has been such a success is ____he never gives up.
 A. what B. where C. how D. that
4. –what is that building?
  -___the garden equipment is stored
 A. that’s where  B. There is in which  C. the building is  D. That’s the building which
5. Our village is no longer ____over twenty years ago.
  A. what was it B. what it was
  C. the village what was D. what was the village
6. ___you are the first one here.
A. it seems that as if B. it seems as if that
c. it seems as if   D. It seems that as though
7. My hope is ___he will become a doctor in the future.
A. if B. whether C. that D. what
8. it was ___they were used as an advertisement for the shop .  
A. because B. which C. what D. if 
1-5DBBAB  6-8 CCA