今天我们来学习一下表语从句，之前我们已经学习过了主语从句和宾语从句，结构上有相似，今天我们一起来看看什么是表语从句？
表语从句
1、用来说明主语的身份、性质、品性、特征和状态。
2、常由名词、代词、数词、动词过去分词、动词的-ing形式、副词、介词短语、形容词、不定式和从句等来充当。
比如以下的句子中表语可以由各种成分充当：
1、The boy talked you just now is my classmate. (名词充当表语)
2、I didn’t know that it was you at that time. (代词充当表语)
3、The window remained closed. (动词-ed充当表语)
4、 My mother’s daily job is cleaning the house. (动词-ing充当表语)
5、The house is not only clean but also beautiful. (形容词充当表语)
6、 When I went to your house, you were out. (副词充当表语)
7、No one was in the room, when he arrived. (介词短语充当表语)
8、My job is to teach you Chinese. (不定式充当表语)
9、The reason why he came late was that he had a stomachache. (从句充当表语)
观察图中两个句子：分清楚主系表结构和主谓宾结构的不同。
我们来分析一下，表语从句的结构：主语+系动词+引导词+简单句，当然注意简单句中句子的语序是陈述语序。
可以连接表语从句的系动词有：
1: be（being,been,am,is,are,was,were)
2: feel ， seem ， look, appear ，sound, taste ， smell
3: stand ， lie ， remain ，keep, stay
4: become ，get ， grow ， turn ，go ，come, run,fall
5: prove, turn out
连接词：that / whether /as if /as though (if不引导表语从句)
连接代词：who / whom / whose / which / what
连接副词：when / where / why / how / because
that
1、 that 在从句中不担任句子成分，无实际意义，一般不能省略
2、在表“建议，劝说，命令”的名词idea, suggestion, request, proposal 等后面的表语从句中，谓语动词用“should + 动词原形”，should可省略。
eg:
My opinion is that it is getting worse and worse.
My suggesstion is that we (should) ride to park early.
2、whether
whether在表语从句中表是否,但不充当句子的成分。if 不能引导表语从句.如:
What the teacher really doubts is whether my mother will come to school soon.
The problem is whether it is worth doing.
3、as if, as though 引导的表语从句
as if/though引导的表语从句常置于连系动词look, seem, sound, be, become等后面，
常用虚拟语气，表示不存在的动作或状态。
e.g. It sounds as if/though somebody was screaming outside.
4、because引导表语从句通常只用于“This/That/It is because…”结构中。
e.g. My joy is because you written to me for a long time.
5、主语为reason 时，表语从句连接词用that, 但以it, this, that 开头做主语的句子，则可用because。
e.g. The reason for his being late was that he missed the early bus.
She was late this morning. That was because she missed the early bus.
最后总结一下：
表语从句的构成：引导词+简单句
引导词包括：连词，连接代词，连接副词
三个注意：1、if不引导表语从句
2、主语为reson时，引导词用that
3、语序为陈述句语序
