在下列情况，通常要用 that：
①当先行词是一个既指人又指物的并列词组时：
I made a speech on the men and things that I had seen abroad.
我就我在国外所见到的人和事作了报告。

②当先行词是who时(为避免重复)：
Who was it that won the World Cup in 1982? 谁赢得了1982年的世界杯？
③当关系代词在定语从句中作表语时(可省略)：
Tom is not the boy (that) he was. 汤姆这孩子已不是以前那个样子了。

3.当先行词是下列不定代词或被它们修饰时much, little, none, all, few, every(thing),
any(thing), no(thing) 等时，通常用that：
All that she lacked was training. 她缺的只是训练。

Have you everything that you need? 你需要的东西都有了吗?
The sleeping man’s subconscious min d retained everything that was said around him. 这位酣睡的人头脑的下意识能记住他周围的人说的话。

She would never do anything that was not approved of by her parents.
她父母不赞同的事她绝不会做。

4.当先行词有the very, the only, the same 等修饰时，通常用that：
This is the only example that I know. 我知道的例子只有这一个。

Those are the very words that he used. 那是他的原话。

5.当先行词有形容词最高级或序数词(包括last, next等)等修饰时，通常用that：
This is the best dicti onary that I’ve ever used. 这是我用过的最好的词典。

The first thing that you should do is to work out a plan.
你应该做的第一件事是订个计划。

6.当关系代词在定语从句中用作表语时，通常用that：
China is not the country (that) it was. 中国已不是过去的中国了。

7.当先行词是一个既指人又指物的并列词组时，通常用that：
They talked about the persons and things that most impressed them.
他们谈论了使他们印象最深的人和事。

8.当要避免重复时：
Which is the course that we are to take? 我们选哪门课程？。