宾语从句：
在句子中起宾语作用的从句叫做宾语从句。
宾语从句分为三类：
动词的宾语从句，介词的宾语从句和形容词的宾语从句。
宾语从句常用的连接词有：
whether that if  what which when how why
例：I don’t know when he will come.
宾语从句的特点：
1、宾语从句可以作及物动词、介词及形容词的宾语；
2、宾语从句的语序一律用陈述句语序。疑问词或者引导词+主语+谓语+其他成分；
例如：I don’t know what they are looking for.
            Could you tell me when the train will leave?
3、连接词that引导宾语从句在句中无词义，不充当句子成份，多数情况下可以省略；
4、whether 和 if 都可引导宾语从句，但 whether后可紧跟or not；whether从句可作介词的宾语；
5、如果从句太长，可以用形式宾语it；
6、时态的一致性。主句和从句的时态要一致。 
主句是一般现在时，从句根据实际情况使用任何时态。
例句：The headmaster hopes everything goes well.
主句是过去时态，从句须用过去时态的某种形式。
例句：She was sorry that she hadn’t finished her work on time.
当宾语从句表示的是一个客观真理或者事实时，即使主句是过去时，从句也用一般现在时态。
例句：The teacher told his class that light travels faster than sound.

宾语从句中引导词的用法:
在复合句中作主句的宾语，引导词有：
连词：that (that 常可省略),whether, if
代词：who, whose, what ,which
副词：when ,where, how, why 等。

（一）that引导的宾语从句（在非正式场合that可以省略）
可跟that从句做宾语的动词有：
say, think, insist, wish, hope, demand, imagine, wonder, know, suppose, see, believe, agree, admit, deny, expect, explain,
order, command, feel, dream, suggest, hear, mean, notice, prefer, request, require, propose, declare, report等。
例句：The boy believes that he will travel through space to other planets.
注意事项：
当主句谓语动词是 think, believe, suppose, expect 等词，而宾语从句的意思是否定时，常把否定转移至主句表示。
例句：I don’t think it is right for him to treat you like that.
在以下情况中that不能省略:
当句中的动词后接多于两个由that引导的宾语从句时，第一个that可省，但后面的that不可省。
例句：He said (that) you were too young to understand the matter and that he was asked not to tell you.
当主句的谓语动词与that宾语从句之间有插入语时，that一般不可省。
例句：Just then I noticed, for the first time, that our master was wearing his fine green coat and his black silk cap.
当that从句是双宾语中的直接宾语时，that不可省。
例句：I can’t tell him that his mother died.
注意事项：许多带复合宾语的句子，that引导的宾语从句经常移到句子后部，而用it作形式宾语。
例句：I find it necessary that we should do the homework on time.

（二）由whether,if 引导的宾语从句
由whether(if)引导的宾语从句，实际上是一般疑问句演变而来的。意思是“是否”。宾语从句要用陈述句语序。
一般说来，在宾语从句中whether与if可以互换使用，但在特殊情况下if与whether是不能互换的。
例句：I wonder whether(if) they will come to our party.
只能用whether，不能用if引导的宾语从句
在带to的不定式前
例句：We decided whether to walk there.
在介词的后面
例句：I’m thinking of whether we should go to see the film.
在动词后面的宾语从句时
例句：We discussed whether we had a sports meeting next week
直接与or not连用时
例句：I can’t say whether or not thet can come on time.
只能用if不能用whether引导的宾语从句
if引导条件状语从句，意为“如果”
例句：The students will go on a picnic if it is sunny.
if引导否定概念的宾语从句时
例句：He asked if I didn’t come to school yesterday.
引导状语从句even if（即使）和as if（好象）时
例句：He talks as if he has known all about it.

（三）连接代词和连接副词引导的宾语从句
这样的宾语从句实际上是由特殊疑问句变化而来的，宾语从句要用陈述句语序。
用于这种结构的动词常常是：see, say, tell, ask, answer, know, decide, show, find out, imagine, suggest, doubt, wonder, discover, understand, inform, advise等。
英语中的连接代词有：who,whom,whose,which,what,在句中担任主语、宾语、定语或者表语。
例句：Can you tell me whom you are waiting for?
英语中的连接副词有：when,where,why,how，在句中担任状语的成分。
例句：None of us knows where these new parts can be bought.