（四）宾语从句
1、宾语从句在复合句中作宾语。引导宾语从句的连词that一般可省略。
e.g. I hope (that) everything is all right.
2、介词之后的宾语从句，不可用which或if连接，要分别用what或 whether。
e.g. I'm interested in whether you've finished the work..
I'm interested in what you've said.
3、whether与if都可以引导宾语从句，常可互换。但下面情况不能互换。
①宾语从句是否定句时，只用if，不用whether。
e.g. I wonder if it doesn't rain.
②用if 会引起误解，就要用whether。
e.g. Please let me know whether you want to go.（此句如果把whether改成if，容易当成条件句理解）
③宾语从句中的whether 与or not直接连用，就不能换成if；不直接连用，可换。
e.g. I don't know whether or not the report is true.
I don't know whether/ if the report is true or not.
④介词后的宾语从句要用whether引导。whether 可与不定式连用。whether也可引导主语从句、表语从句、同位语从句，还可引导让步状语从句，以上均不能换成if。但引导条件从句时，只能用if，而不能用whether。
e.g. It depends on whether we have enough time.
They don't know whether to go there.
Please come to see me if you have time.
（五）同位语从句
同位语从句在句中作某一名词的同位语，一般位于该名词（如：news, fact, idea, suggestion, promise等）之后，说明该名词的具体内容。
e.g. I have no idea when he will be back.
The fact that he had not said anything surprised everybody.