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1. must 的三种用法:

1) 必须, 千万要…

否定为 must not

You mustn't go to dangerous places.

2) 必须, 要(口气没有那么重)

否定为: need not

---Must I go?

---No, you need not.

3) 一定, 大概(表示推测)

现在时: must do

过去时: must have done

You must be a worker (now).

You must have been a worker 10 years ago.( past)

否定:cannot or could not都可以。考试时，cannot最好用于现在时，could not最好用于过去时：

You cannot be a worker (now).

You could not have been a worker 10 years ago .( past)

问句can 或could:

---Can he be a worker (now)?

---Yes, he must.

---No, he can't



---Could he have been a worker 10 years ago ( past)?

---Yes, he could.

---No, he could not.

2 虚拟句型：

1〕基本句型


从句
主句

过去
If…had done…
…would have done…

现在
If…were/did…
…would do…

将来
If…were to/should do…
-…would do..








If I had passed the math test, I would have felt happier yesterday.

If I were a bird, I could fly.

If he came today, he could join us.

If it were to rain tomorrow, I would not go to Beijing.

If it should rain tomorrow, I would not go to Beijing.

2〕"拧麻花"（从句随从句的时间，主句随主句的时间）

If I had passed CET-4 test last year, I would not take another one next year

.

3) 省略与倒装

A) 删去"if";

B) "had","should"，"were"放在从句句首。

C) 其余照抄。

Had I passed the math test, I would have felt happier yesterday.

Were I a bird, I could fly.

Were it to rain tomorrow, I would not go to Beijing.

Should it rain tomorrow, I would not go to Beijing.

但"did"不可提前：

If he came today, he could join us.

（病句）Did he come today, he could join us.×××

4) 注意省略与倒装的从句在后面时的句型辨认：



I would have felt happier yesteday ___I passed the math test.

A) did B) had C) should D) were

应该选 B)。



I would have felt happier yesterday had I passed the math test.

I could fly were I a bird.

I would not go to Beijing were it to rain tomorrow.

I would not go to Beijing should it rain tomorrow.