2.The most important thing that should be done right now is how to stop him from going on.

(5) 先行词既有人又有物，用which和who都不适合，这时宜用that. 如：

1.This is the best that can be done now.

2.This is the third film that has been shown in our school this term.

(4) 先行词是最高级或被最高级修饰时。如：

1.When we talk about Wuxi, the first that comes into mind is Tai Lake.

6.比较 *This is one of the best novels that were published last year.

　　　　 *This is the only one of the best novels that was published last year.

(3) 先行词是序数词时或被序数词修饰时。如：

5. I hope the little that I can will be of some help to them.

4. You can take any (=whichever) seat that is free.

3.The last place (that) we visited was the chemical works.

2.That's the very word that is wrongly used.

1.The only thing that we could do was to wait.