初中英语――if引导的条件状语从句
引导条件状语从句最常用的连词是if，常见的if条件状语从句表示在某条件下，某事很可能发生，条件是可能存在的，主句中某种情况发生的概率也是很高的。如：
If you ask him，he will help you．如果你请他帮忙，他会帮你的。
If you fail in the exam，you will let him down．如果你考试不及格，你会让他失望的。
If you have finished the homework，you can go home．如果你作业做完了就可以回家了。
另外，if从句还表示不可实现的条件或根本不可能存在的条件，也就是一种虚拟的条件或假设。从句多用一般过去时或过去完成时，表示对现在或过去的一种假设。如：
If I were you，I would invite him to the party．如果我是你，我会邀请他参加聚会。
I would have arrived much earlier if I had not been caught in the traffic．要不是交通堵塞，我本会来得早一些。
另外你还要注意if 条件句的时态搭配
1．if从句用一般现在时，主句用一般将来时
If he runs he’ll get there in time. 如果他用跑的，他就会及时赶到那儿。
The cat will scratch you if you pull her tail. 如果你拉猫的尾巴，它就会抓你。
2．if从句用一般现在时，主句用may/might/can
If the fog gets thicker the plane may/might be diverted. 如果雾在大一些，飞机可能就会改在别的机场降落。
If it stops snowing we can go out. 如果雪停了，我们就可以出去。
3．if从句用一般现在时，主句用must/should
If you want to lose weight you must/should eat less bread. 如果你想减肥，你必须少吃面包。4．if从句用一般现在时，主句用一般现在时
If you heat ice it turns to water. (也可用will turn)如果把冰加热，它就会化成水。
5．if从句用现在进行时，主句用一般将来时
If you are looking for Peter you’ll find him upstairs. 如果你是在找彼得，上楼就会找到他。6．if从句用现在完成时，主句用一般将来时
If you have finished dinner I’ll ask the waiter for the bill. 如果你吃完了，我就叫服务生来算账
注意：
学习" if " 引导的条件状语从句的用法,现在总结一下:
if 条件句不一般,几个要点记心间;
条件句,放在前,逗号要放句中间。
条件句表可能，主句多用将来时；
条件句表事实，主句常用现在时。
在if 引导的条件状语从句中，如果从句谈论的是一个有可能发生的事实及其产生的相关的结果，主句用一般将来时态，从句用一般现在时态。如：
We can walk there if we can't find a bus .
If it rains tomorrow ,we will not go to the zoo.
What will you do if you find a panda in danger.
如果if 条件句谈论的是重复发生和预示要发生的情景和事件，则主从句大多用一般现在时态。如：
If bears are in danger ,they attack people.
在if 引导的条件状语从句中，if 和条件句位置灵活，可直接放在主句后面，若if 条件句放句首，从句后面要加逗号，和主句隔开。还要注意前后时态一致原则
if 条件状语从句的时态练习
一．在正确的答案下划一条线。
1.Daina ( will go/go/goes) to Europe if she (will pass/pass/passes) the exams .
2. The graduates (will teach/teach/teaches) in the poor village if the Ministry of Education (will agree/ agree/agrees) soon.
3. If there (will be/ are/is) a car accident, they (will call/call/calls) 110 for help at once.
4. If it (won’t/don’t/doesn’t/ isn’t) rainy, we (will take/ take/takes) walk outside.
5. If a UFO (will land/land/lands) in front of me, I (will go/go/goes) in to look for the alien.
6. If he (will have/have/has) money, he (will bulid/build/builds) a science lab.
7.Don’t wait for me if I (am/ will be) late.
8.They (won’t/don’t) go to the beach if it (will rain/rain /rains).
9. I (will call/ call) you if he (will stay/stay /stays) at home.
10. Mr Smith (will let/ let/lets) you know if he (will need/ need/ needs) help.
11. (Will / Do/ Does) he visit the museum if he (won’t / don’t/ doesn’t) get tired?
12. Where (will/ do/does) they live if they (will miss/ miss/ misses) the bus?
二、用所给词的适当形式填空
1.If you ________(feel) tired, you _______________ (have) to have a rest.
2. Where _______ he _________(see) the film if he ________________(have) time?
3. If there __________(be) fewer trees, there _______________( be) more pollution.
4. He _____________(dress) more casually if he ________________( not work) on weekends.
5. If Marcia _____________(live) alone, she ___________________( keep) a pet parrot.
6. Lana ________________( buy) a new dress if the old one ____________(be) out of style.
7.The twins ______________(fight) if they_______________(argue).
8. I ____________(have) a bake sale if I _____________(need) money for education.
9. Peter _____________( send) me a beautiful souvenir if he ________________(tour) Spain.
10. If Mr Green ___________(say) I am hard- working, my parents _________( feel) glad.
11.I ____________(go) to the beach if it________________ ( not rain) this week.
12. __________they __________( have) a match if the P.E. teacher _____________(be) busy?
13.He ____(write) a letter to his grandparents if he ____(get) his report card this week.
14. If she ____________(get) up late, she _____________ ( not catch) the early bus.
15. Peter ________(major) in English if he ____(pass) the exams in Peking University.
15.如果他到的晚了会发生什么事情？What _______________ if he _____________ late?
16. 如果努力学习，你就会取得好成绩。
If you__________ _________, you ___________ good _____________.
17. 他如果看电视太久了，他的父母会不高兴。
If he _________ TV too much, his parents __________ __________ unhappy.
18. 如果我们为他组织生日聚会，大家都会来的。
Everyone ________________ if we _____________ a birthday party __________ him.
19. 如果明天不下雨，我会和你一起去公园的。
If it __________ __________ tomorrow, I ______________ go to the park _________ you.
