1．当主句和从句所表示的是原理、客观真理、
规则时，主句是一般现在时（包括祈使 句和含有情态动词can/may/must等）， 从句也要用一般现在时。
例如： 1) If you put a piece of paper into water, it gets wet．如果你把一张纸放进水中，它 会变湿。(原理)
2. Where _______ he _________(see) the film if he ________________(have) time?
3. If there __________(be) fewer trees, there _______________( be) more pollution.
1） 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。
2） 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。
it____(die). 10. Don't go out tomorrow if it ______(rain).
二、同义句转换
1. Play some sports, and you'll be healthy. ____ _____ play some sports, you'll be
healthy. 2. If you study hard, you will catch up with
So I hope all of us will try to follow these: Never throw rubbish everywhere. Don't step on the grass or pick flowers near the beach. In a word, beaches are an important part of our living environment; we all need to try our best to protect them. （小结）
2)Be careful if you cross the road.(祈使句)
3) You must see the doctor if you are ill.( 含有情态动词）
2. 在if条件状语从句中，如果从句谈论的是一
个可能发生的事实及其产生的相关结果，主 句用一般将来时，从句用一般现在时。
三 根据汉语提示完成句子
1.如果我有时间的话，我就会去帮你。 If I ___ ___,I ___ ___ you with it.
2.如果明天不下雨，我们就去徒步旅行。 If it ___ ___ tomorrow,we'll go hiking.
3.我们没有人能赶上汤姆，除非他不跑。 None of us can ___ ___ ___ Tom ___ he does't run.
6. If you ______(need) the instructions in English, go to our website.
7. If the green light______(not be) on, we must wait for one minute.
8. I don't know if he_____(come) tomorrow. 9. If you don't put fish back to water,
In my opinion, these strict rules can help us create a better beach environment. The beaches will be cleaner and more beautiful if each tourist can realize the imoportance of protecting them.
2. unless也可引导条件状语从句，相当于 if...not，意思是“如果不、除非”。 例如：
You will fail in Math unless you work harder.
= You will fail in Math if you don't work harder. 你要是不再加把劲儿，数学考试就不及格了。
一、什么是条件状语从句？
在某种条件下，可能发生某事。而由 if/unless引导的表示条件的句子，就叫条件 状语从句。 eg: If you get up early, you will catch the bus.
If you put wood into water, it floats.
二、时态
1、当主语是you时,if引导的条件状语从句可 与“祈使句+ and／or+简单句”进行句型 转换。and表示句意顺承；or表示转折，意 为“否则”。
例如：
Take care, or you'll fall off the tree. 小心，否则你会从树上掉下来。
=If you don't take care, you'll fall off the tree.
Thank you for your listening. Have a nice weekend!
2. if表示“是否”时引导宾语从句，意思同 whether. I dont' know if he can come. If he comes, I' ll tell you at once.
一、用括号内单词的适当形式填空
1.If you ________(feel) tired, you _______________ (have) to have a rest.
4. He _____________(dress) more casually if he ________________( not work) on weekends.
5. If Marcia _____________(live) alone, she ___________________( keep) a pet parrot.
As we know, beaches are great places for us to travel and relax. In order to protect the beaches, our government has made some strict rules. However, some citizens don't understand it.
三、条件状语在句中的位置
大多数情况下，if/unless从句既可以放在 主句之前也可以放在主句之后。当从句置于 主句之前时，常用逗号与主句隔开。
It floats if you put wood into water.=If you put wood into water, it floats.
四、转换
4.他不会迟到的，除非他生病。 He ___ ___ late ___ he ___ ill. 5.如果你看见汤姆，叫他来我办公室。 ___ Tom to come to my office ___ you
___ him.
Good morning, ladies and gentlemen! May I have your attention,please? I'm a volunteer and I'm glad to tell you something about protecting the beaches in Shenzhen.
your classmates. _____ you study hard, you won't catch up
with your classmates. 3.Fish will die without water. Fish will die _____ there is no water.
4.Don't stay up later,or won't be sleepy tomorrow.
条件状语从句
预习：
1. 什么是条件状语从句？ 2. 条件状语从句如何与主句时态搭配？

条件状语从句
经典例句：
1. If you stick a pin into a balloon, it bursts.
2. Unless you keep ice cream in a fridge, it melts.
五、拓展
1. if从句还可以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，主句则用虚拟语气。
1) If I were you, I would invite him to the party. 2) I would have arrived much earlier if I had not been caught in the traffic.
____ you ____ stay up late,you won't be sleepy tomorrow.
5.I will come to see you unless I am too busy.
____ I am ____ too busy, I will come to see you.
eg:
1) If it rains tomorrow, we will not go to the zoo.
2) If you go to bed earlier, you won't feel tired in the morning.