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八年级英语人教版·上册
Section A (Grammar)
Unit 8
Let’s communicate!
一、新课引入
If you walk to school, you’ll be late.
If you don’t take part in the football match, you will be sorry.
一、新课引入
Connect the sentences with “if”.
I will go to the party tomorrow.
I will have a good time tomorrow.
If I go to the party tomorrow, I’ll have a good time.
He will be free next Sunday.
He will go fishing with his grandfather.
If he is free next Sunday, he will go fishing with his grandfather.
二、新课讲解
if引导的条件状语从句
条件状语从句可由连词if引导，意为“如果；假如；倘若”，表示在某种条件下很可能会发生某事或不发生某事。
二、新课讲解
if引导的条件状语从句
1. if引导的条件状语从句的位置
if引导的条件状语从句的位置比较灵活，可放在主句前面，也可放在主句后面。若放在主句前，从句后面要用逗号和主句隔开。
If he doesn’t feel tired, he will visit the museum. = He will visit the museum if he doesn’t feel tired. 如果他不感觉累，他将会去参观博物馆。
二、新课讲解
if引导的条件状语从句
2. if引导的条件状语从句的时态
(1) 当主句用一般将来时时，if引导的条件状语从句要用一般现在时。
If it rains tomorrow, I won’t climb the hills. 如果明天下雨，我就不爬山。
二、新课讲解
if引导的条件状语从句
(2) 当主句中含有can, may, must等情态动词时，if引导的条件状语从句要用一般现在时。
We can win the basketball game if he joins us. 如果他加入我们，我们就能赢得这场篮球赛。
二、新课讲解
if引导的条件状语从句
(3) 当主句是祈使句时，if引导的条件状语从句要用一般现在时。
Help your mum with the housework if you finish your homework early. 如果你家庭作业完成得早，就帮你妈妈做家务。
二、新课讲解
if引导的条件状语从句
3. 与其他句式之间的转换
(1) 与“祈使句+and/or+一般将来时的句子”这一句型相互转换。
If you get up early, you’ll get there on time. = Get up early, and you’ll get there on time. = Get up early, or you won’t get there on time. 如果你早点儿起床，你就会准时到那里。
二、新课讲解
if引导的条件状语从句
(2) 借助介词without或with来转换。
If there is no water, fish will die. = Fish will die without water. 如果没有水，鱼就会死。
If you help me, I’ll finish the work soon. = With your help, I’ll finish the work soon. 如果你帮助我，我很快就会完成工作。
二、新课讲解
if引导的条件状语从句
(3) 与unless引导的条件状语从句相互转换。
You will be late if you don’t go there by bus. = You will be late unless you go there by bus. 如果你不乘公共汽车去那儿，你就会迟到。
二、新课讲解
if引导的条件状语从句
4. 注意事项
(1) 在if引导的条件状语从句中，当主句是一般将来时态时，不能使用be going to结构，而要用will。
I’ll help you with your English if I am free tomorrow. 如果明天我有空，我会帮你学英语。
二、新课讲解
if引导的条件状语从句
(2) 在if引导的条件状语从句中，如果从句谈论的是一件有可能发生的事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；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、从句均用一般现在时。
If it rains tomorrow, we won’t go to the zoo. 如果明天下雨，我们就不去动物园。
If bears are in danger, they attack people. 如果熊遇到危险，它们就会攻击人类。
二、新课讲解
if引导的条件状语从句
5. if引导条件状语从句与if引导宾语从句时的区别
if引导条件状语从句时，表示“假如；如果”，条件状语从句可位于句首或句末。if引导宾语从句时，表示“是否”。
If it doesn’t rain tomorrow, we will go hiking. 如果明天不下雨，我们就去远足。
Please tell me if you know the answer. 请告诉我你是否知道答案。
三、归纳小结
if引导的条件状语从句
四、强化训练
一 、单项填空
( ) 1. You should eat more vegetables and fruits _______ you want to keep fit.
A. but B. so C. if D. and
( ) 2. Please raise your hand _______ you agree with us.
A. unless B. if C. although D. before
( ) 3. —Amy says she _______ a seaside city to spend her holiday if she _______ enough time.
—Great! Seaside cities are truly attractive places.
A. will choose; has B. chooses; will have
C. chooses; has D. will choose; will have
C
B
A
四、强化训练
二 、完成句子
1. _________ you come to the party, you will enjoy yourselves.
2. _________ (add) some hot water if you think the tea is too strong.
3. Shall we go out for a picnic if it _________ (not be) rainy tomorrow?
4. If he misses the train, he ___________ (be late) for the meeting.
5. I don’t know if it will snow tomorrow. If it _________ (snow), we’ll make snowmen.
Add
If
isn’t
will be late
snows
四、强化训练
三、句型转换
1. The traffic lights are red. We must wait. (用if合并为一句)
_________ the traffic lights are red, we must wait.
2. 如果明天不下雨，我们就去游玩。(补全句子)
We will go on a trip _________ it ________ rain tomorrow.
3. Use your mind, and you will find a way out. (改为条件状语从句)
_______________________, you will find a way out.
If
If you use your mind
if
doesn’t
四、强化训练
4. Don’t play on the street, or you will be in danger. (改为同义句)
_________ you _________ on the street, you will be in danger.
5. Nobody can live without air or water. (保持句意不变)
_________ there is _________ air or water, nobody can live.
6. You’ll fail the exam unless you work hard. (改为同义句)
_________ you _________ work hard, you’ll fail the exam.
play
If
no
If
don’t
If

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