语法点拨：if与unless引导的条件状语从句
1．常用引导词：if（如果），unless（除非）。

I won’t go to the movies unless I am free tomorrow.
除非我明天有空，否则我不会去看电影。

2．条件状语从句的位置
可放在句首或句尾，放在句首时常用逗号与主句隔开。

e.g.If it rains tomorrow, I will stay at home.
= I will stay at home if it rains tomorrow.
如果明天下雨我就呆在家里。

3．if引导词用法
if引导的条件句有：真实条件句和非真实条件句两种。

真实条件句：表示在某种条件下某事很可能发生。

e.g.If you ask him, he will help you.
如果你请他帮忙，他会帮你的。

4．unless引导词用法
固定搭配：unless=if...not 除非，若不，如果不
e.g.You will fail to arrive there in time unless
you start earlier.
=If you don’t start earlier, you will fail to
arrive there in time.
如果你不早点动身，你就不能及时赶到
那儿。

注意：在含有条件状语从句的复合句中，当主句是一
般将来时态，从句要用一般现在时（即主将从现原
则）。

如果主句是祈使句或含有情态动词时，从句也
用一般现在时表将来。

e.g.If you study hard, you will pass the exam.
1. I will send you an e-mail as soon as I ____A___ in Canada.
A. arrive
B. arrived
C. am arriving
D. will arrive
2. If there ____A___ no buying and selling of animals, there ______ no killing in nature.
A. is; will be
B. will be; will be
C. is; is
D. will be; is
3. I’m waiting for my friend.__C___, I'll go shopping alone.
A. If she comes
B. If she won't come
C. If she doesn't come
5. You can’t watch TV ___A_____ you finish your homework.
A. unless
B. if
C. while
D. as
7.The students _____A___ have a sports meeting this weekend if it __ _.
A. won’t; rains
B. will; rains
C. won’t; will rain
D. are going to; is going to rain
9. I don't know if she ____B___ to my birthday party tomorrow. If she ______, I'll be very happy.
A. comes; comes
B. will come; comes
C. comes; will come
10. — When will you come to Daqing? — I will call you ___D__I arrive.
A. till
B. while
C. as quickly as
D. as soon as
11. I’ll give it to Jim as soon as I ___C____ him tomorrow.
A. saw
B. will see
C. see
D. have seen。