宾语从句即指在主从复合句中用作宾语的从句。宾语从句通常由连词that和whether (if)以及连接代词或连接副词引导。宾语从句的词序要用陈述句词序，不能用疑问句词序。

宾语从句的引导词

(1) 用that引导。that只起引导词作用，不充当句子成分，也没有词义，且通常可以省略：

We think (that) he will help us. 我们认为他会帮助我们。

He said (that) he was good at English. 他说他擅长英语。

I know (that) he is very busy. 我知道他很忙。

(2) 用if或whether引导。if和whether引导宾语从句，不充当句子成分，但有词义，表示“是否”：

I don't know if [whether] he will come. 我不知道他是否会来。

She asked if [whether] that was enough. 她问那是否够了。

I wonder whether [if] it is true. 我不知道是不是真的。

(3) 用连接代词引导。常见的引导宾语从句的连接代词有what, who, whom, which, whose等。此时要特别注意宾语从句用陈述句词序，而不用疑问句词序：

Ask him which he wants. 问他要哪一个。

She asked who would like to go. 她问谁愿意去。

Tell me whose wallet this is. 告诉我这是谁的钱包

【注】what引导宾语从句时，有时表示“什么”，有时表示“…所…的”。比较：

I asked what he needed. 你问他需要什么。

I gave him what he needed. 我给了他所需要的东西。

(4) 用连接副词引导。常见的引导宾语从句的连接副词有when, how, where, why等。此时要特别注意宾语从句用陈述句词序，而不用疑问句词序：

He knows where they live. 他知道他们住哪里。

Tell us how you are getting on now. 告诉我们你现在过得怎样？

I can't tell you why she is crying. 我不能告诉你她为什么哭。

He didn't say when he would return. 他没有说什么时候回来。