三.宾语从句的三种基本形式：
1.从属连词that引导
that无词义，不充当句子成分，可省略。
如：He told me (that) he was ill.他告诉我他生病了。
注意：以下情况that不能省略
①主句的谓语*连接多个宾语从句时，第一个that可以省略，而其他的that不能省略。
如：I think (that) it will be sunny tomorrow and that we will go shopping.我认为明天是晴天，我们将去购物。
②that 引导的宾语从句作介词宾语时，that不能省略。
如：I know nothing about her except that she is a teacher.我对她一无所知，只知道她是个老师。
③that引导的宾语从句和主句的谓语*之间有插入语时，that不能省略。
如：I remembered,first of all,that I lost my USB.我记起来了，尤其重要的是，我弄丢了优盘。
④that 从句位于句首时，that不可省略。
如：That he ever did such a thing I simply don't believe.我简直不相信他做了这样的事。
⑤当宾语从句的主语是his,that或有his和that修饰时。
如：Lucy that me that that was why she was late.露西告诉我那就是她迟到的原因。
2.从属连词if/whether引导
一般情况下可以相互替换，在口语中多用if，不充当句子成分，有具体的含义“是否”。
如：I don't know if you can help me.我不知道你能否帮助我。
I doubt whether he will get there on time.我怀疑他能否准时到那儿。
注意：以下情况只能用whether不可用if
①与or not 连用
如：I wonder whether it is true or not.我想知道它是真是假。
②在介词后
如：It depends on whether it is going to rain.它取决于是否天会下雨。
③在不定式前
如：Whether to go there or not hasn't been decided.是否去那儿还没有决定下来。
④if 引导的宾语从句如果会引起歧义，应避免用if而用whether
如:Please let me know if you want to go.
Please let me know whether you want to go.
3.连接代词或连接副词引导
连接代词：who,whom,whose,what,which,whoever,whatever,whichever
连接副词：where,when,how,why
在句中充当句子成分，不可省略。
如：You can do what you want.你可以*。
I don't know whose box this is.我不知道这是谁的盒子。
四.宾语从句的其他用法
1.it作形式宾语代替宾语从句
I think it necessary that we take enough water every day.我认为每天喝足够的水是必要的。
We take it for granted that we should go to work on time.我们把按时上班视为理所当然。
2.某些形容词或过去分词后加宾语从句
如：aware,certain,afraid,pleased,satisfied,glad,proud......
I'm sorry that I've made a mistake.
3.宾语从句的否定转移
若主句谓语*有think,consider,believe,suppose,expect,guess,imagine等，其后的宾语从句若含有否定意义，一般要把否定词转移到主句谓语上，从句谓语用肯定式。
I don't think you are right.我认为你不对。
4.宾语从句的语序
宾语从句要用陈述句语序。
Can you tell me what they are doing?(√)
Can you tell me what are they doing?(x)
5.宾语从句的简化
I don't know what I can do.=I don't know what to do.
Tom hopes that he will be back soon.=Tom hopes to be back soon.
Could you tell me how I can get there?=Could you tell me how to get there?
6.宾语从句的时态
①主句是一般现在时，从句可根据需要选择相应的任何时态。
I don't know when he will come back.
He says that he went to Beijing last month.
②主句是一般过去时，从句要用相应的过去时态。
He said that he went to Beijing last month.
③如果宾语从句表示的是客观事实，普遍真理，自然现象，习惯性动作等，不管主句是什么时态，从句都用一般现在时。
The teacher said that the earth goes round the sun.老师说，地球绕着太阳转。