1．so或not可替代that从句。so替代肯定的that从句；not替代否定的that从句，通常与I'm afraid / believe / expect / fear / guess / hope / suppose / think等搭配。例如：

- Have we got enough time?

- I think so. (= I think we have enough time.) / I think not. (= I don't think we have enough time.)

- We can't finish the work on time.

- I suppose not. (= I suppose that we can't finish the work on time.)

2．so与not可用来代替if 后面的从句，构成if so / if not省略句。例如：

Are you free this weekend? If so (= If you are free this weekend), I want to invite you to go to the cinema.

Are there any books about Lu Xun in the library? If not (= If there are not any books in the library), I will buy one in bookstores.

3．not可与perhaps，possibly，probably，certainly，surely等副词搭配，用来替代句子。但是so不可以这样用。例如：

- Are you satisfied with his idea?

- Certainly not. (= Certainly I am not satisfied with his idea.)

4．it也可以替代一个句子。例如：

If you don't try your best, you'll regret it. (= you will regret that you don't try your best.)

单元各部分分类练习

Section 1

New words and ideas

请从每道题的四个选项中选出一个最佳选项。

　1. I was about to put up my hand __________ Susan stood up and gave her answer.

　　A. when B. while C. since D. before

　2. The living geography lesson we had been looking forward to __________ yesterday.

　　A. being given B. giving C. was given D. gave

　3. The students stood around their chemistry teacher silently, with their eyes __________ what he was doing.

　　A. fixed on B. fixing on C. were fixed on D. were fixing on

　4. _________ we all know, the earth travels around the sun.

　　A. Which B. With C. As D. What

　5. I've been thinking what __________ one an excellent teacher.

　　A. becomes B. makes C. turns D. forms

　6. He has realized the trouble he will have ___________ the problem.

　　A. solved B. to solve C. solving D. solve

　7. He tried his best to get everything finished on time. ________________.

　　A. Neither did we B. So do we

　　C. So did we D. So we did

　8. He said nothing about your work. __________, he was not satisfied with your work.

　　A. To begin with B. Simply put

C. In his opinion D. To tell you the truth