从属连词：有两个that和whether，that和whether在表语从句中不作任何成分，that无实义，whether仍然“是否”的含义
The reason for his absence was that he was ill in hospital.
The question is whether they will able to help us out.
连接代词：who,whom,whose,what,which,whoever,whomever,whosever,whatever,
whichever等
That is what we should do first.
The doubt is who has got away with the document.
连接副词：when,where,why,how,whenever,wherever,however等
That was where we camped last time.
The question is however we can do the work better.
其他连接词：从属连词if不用来引导表语从句，但
as if,as,because,like,as though等可以连接表语从句
Things are not as they seem to be.
The old man looked at the picture,he felt as though he had gone back to 20 years ago.
特别提醒：
the reason why+句子+is that+从句 ....的原因是.....
That's why+结果：这就是为什么.....
It is because+原因：这是因为.....
虚拟语气
如主句的主语是idea,advice,suggestion,order,request等名词时，主语无论是单数还是复数，表语从句谓语一律用：（should）+动词原形
My suggestion is that we (should) have a discussion about this matter.
I just got word that he isn't coming this evening.
We haven't yet settled the question where we are going to spend our summer vacation.
与定语从句的区别
that作为引导词
表达的内容不同：
定语从句用来说明名词的性质 特征 来源等
The fact that he presented was a strong proof.
同位语从句用来说明名词的具体内容，进一步解释
The fact that she hadn't said anything surprised us all.
语法作用不同：
定语从句中that是关系代词，指代上文的人或物，指代物时可以which代替
We expressed the hope that Mr.Smith would come to visit China.
同位语从句中that是连词，不可省略，不可以用which代替
The news we heard spread all over the country.
一招定同从句辨析：
将”名词+that“结构取出来，能在名词和that中间加上be动词的结构是同位语从句
The news that Russia had solved the problem spread all over the world.
The news is that Russia had solved the problem spread all over the world.
定语从句则不能在”名词+that“结构中间加上be动词
I have got some news that you may not have heard.
when,where,why
when,where,why引导定语从句时，分别指前面先行词所表示的时间 地点 原因
I shall never forget the days when we worked on the farm.
when,where,why引导同位语从句则是用来解释和说明先行词的具体内容的
The question where we should go hasn't been discussed.
