条件状语从句
常用引导词：if, unless, as/so long as
1、if 从句+ 祈使句，“如果……，就……”
If you do not feel well, please go to see the doctor. 如果你感觉不舒服，就去看医生吧。
If you want to know more about it, call now. 如果你想了解更多内容，现在就打电话吧。
Make sure you visit the Science Museum if you ever go to London. 如果你去伦敦，一定要去参观科学博物馆。
2、主将从现
If I start after dinner, I’ll finish it before I go to bed. 如果我晚饭后开始，睡觉前我就能完成。
主句也可用“情态动词+ 动词原形”
She may come with us if she arrives in time. 如果她来得及时，就可以和我们一起去。
3、if条件状语从句和并列句的转换
Hurry up, or you’ll be late. = If you don’t hurry up, you’ll be late.
Study hard and you will pass the exam. = If you study hard, you will pass the exam.
练习
（一）句型转换
1. Run fast, or you’ll be late for school.
_______ you _______ _______ fast, you’ll be late for school.
2. You can buy the dictionary if you take enough money with you.
Take enough money with you, _______ _______ _______ buy the dictionary.
3. If there is no air, none of us can live.
None of us can live _______ _______.
4、unless “除非”
Don’t leave the building unless I tell you to. 不要离开大楼，除非我准许。
Unless you have finish ed your homework, I won’t allow you to watch TV. 除非你已完成了作业，否则我是不会让你看电视的。
unless = if not
You’ll be late if you don’t hurry. = You’ll be late unles s you hurry.
I can’t catch the train if I don’t get up early. = I can’t catch the train unless I get up early.
练习
（一）if not与unless相互替换
1. He will not go unless I come with her.
_____________________________________________
2. If you don’t finish it, I will be angry.
_____________________________________________
3. Unless I am mistaken, I’ve seen that man before.
_____________________________________________
4. You won’t get a good job, unless you work hard.
_____________________________________________
5. Unless the strike has been called off, there will be no trains tomorrow.
__________________________________________________________
5、as/so long as 只要
You may use my dictionary as/so long as you don’t keep it too long.只要使用时间不太长，你可以用我的词典。
You can take my car as/so long as you drive carefully. 你可以用我的汽车，只要你小心点儿开。
练习
（一）用if或unless填空
1. ________ he wants to see me, you can tell him to wait.
2. ________ it snows tomorrow, we’ll have a day or two off.
3. We won’t go to his party ________ he invites us.
4. She is sure to pass the examination ________ she is ill.
5. I’ll take that computer ________ I have enough money.
6. ________ my grandma wears glasses, she can see better.
7. I won’t buy that backpack ________ it costs less than $20
8. ________ I’m tired; I’ll have a rest for tea.
9. You won’t get paid for time off ________ you have a doctor’s note.
10. You will get a toothache ________ you do clean your teeth regularly.
（二）用所给单词的适当形式填空
1. If he ________ (get) a low mark in the test, he ________ (study) harder.
2. If you ________ (swim) every day this summer, you ________ (be) very healthy.
3. If he ________ (not hurry), he ________ (not see) the beginning of the match.
4. You can’t go out unless you ________ (finish) your homework.
5. Unless I save my money carefully, I ________ (not be) able to buy a football.
6. If it ________ (not rain) tomorrow, we ________ (go) to the park.
7. If he ________ (return) to the school, I ________ (let) you know.
8. He ________ smoke unless he ________ (have) enough money.
