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教学课件
沪教（牛津）英语八年级下册
Unit8语法专项—— 原因状语从句
全解精讲+分层练习
学习目标
理解原因状语从句的基本功能与使用场景。
掌握 because / as / since 引导从句的用法与语气差异。
明确区分 because 与 because of 的不同使用规则。
能正确摆放从句位置并规范使用标点。
在各类题型中准确运用本单元语法知识。
原因状语从句概念
原因状语从句用于说明主句动作发生的原因。
由连词引导，不能独立成句，必须依附主句。
本单元重点连词：because、as、since。
另有短语类原因标志：because of。
常用于解释理由、叙述事件、说明情况。
because 用法讲解
because 意为“因为”，语气在三者中最强。
专门用于回答 why 引导的特殊疑问句。
强调最直接、最核心、最有说服力的原因。
可置于主句前或主句后，位置灵活。
例句：He didn’t go to school because he was ill.
because 位置与例句
because 引导的从句放在句首时，后面加逗号。
例句：Because it rained heavily, we stayed at home.
用于回答 why 问句时，只能用 because。
例句：Why are you late Because I missed the bus.
它是表达原因最常用、最强调的连词。
as 用法讲解
as 意为“由于、既然”，语气比 because 弱。
侧重陈述显而易见、双方已知的原因。
通常放在句首使用，语气自然平和。
不用于回答 why 提出的问题。
例句：As it was dark, we had to stop our work.
as 常用例句
As you don’t know the truth, I will tell you.
既然你不知道真相，我来告诉你。
As the weather was bad, we put off the plan.
由于天气恶劣，我们推迟了计划。
As you are tired, you can have a good rest.
既然你累了，就好好休息一下。
since 用法讲解
since 意为“既然、由于”，语气较弱。
强调基于已知事实、公认理由给出推断。
用法与 as 高度接近，常可互换使用。
多用于句首，不用于回答 why 问句。
例句：Since everyone is here, let’s begin.
since 常用例句
Since you like reading, you can take this book.
既然你喜欢阅读，你可以拿走这本书。
Since you have finished your work, you can leave.
既然你完成了工作，就可以离开了。
Since no one agrees, we have to change the idea.
既然没人同意，我们只好改变想法。
because / as / since 对比表
连词 语气 用法特点 常用位置
because 最强 回答why，强调直接原因 句首/句末
as 较弱 已知原因，陈述事实 多在句首
since 较弱 既然，显而易见理由 多在句首
从句位置与标点规则
原因状语从句可放在主句前或主句后。
从句在句首：连词+从句，+主句。 Because he was scared, he ran away.
从句在句末：主句+连词+从句。 He ran away because he was scared.
句首从句末尾必须加逗号。从句在前：As it was late, we went home.
句末从句前一般不加逗号。从句在后：We went home as it was late.
句意不变，仅强调重点略有不同。
because of 用法讲解
because of 意为“因为、由于”，是短语介词。
后面只能接名词、名词短语或代词。
绝对不能接完整的句子，这是高频考点。
可与 because 引导的从句进行同义改写。
例句：They didn’t go out because of the heavy rain.
because 与 because of 转换规则
because + 完整句子
because of + 名词/名词短语
两者可进行同义句转换。
例句：Because it snowed heavily, we stayed at home.
= Because of the heavy snow, we stayed at home.
常见错误提醒
because 是连词，后必须接完整句子。
because of 是介词短语，后只能接名词类。
错误表达：because of it rained heavily.
错误表达：because the bad weather.
as / since 不用于回答 why 问句。
拓展知识：for 用法简介
for 也可表示原因，属于并列连词。
语气最弱，仅补充说明理由。
只能放在主句后，前面常用逗号隔开。
例句：He didn’t go out, for it was too late.
习题一：选词填空
用 because / as / since / because of 填空
1.I didn’t go there ___________ I was busy.
2.___________ you are right, I will follow you.
3.She was late ___________ the heavy traffic.
4.___________ it was cold, he wore a thick coat.
5.They were happy ___________ they won the game.
because
Since / As
because of
As / Since
because
6.___________ you don’t know it, I will tell you.
7.The meeting was put off ___________ the storm.
8.He didn’t come ___________ his mother was ill.
9.___________ it was getting dark, we hurried home.
10.She cried ___________ she lost her new bike.
Since / As
because of
because
As / Since
because
习题二：用所给内容完成句子
1.He stayed at home ________________ (because / it snowed).
2.She was excited ____________________ (because of / the good result).
3.________________ (as / it was cold), he wore warm clothes.
4.__________________ (since / you know him), you can help me.
5.We stopped ____________________ (because / it was too late).
because it snowed
because of the good result
As it was cold
Since you know him
because it was too late
习题三：单项选择
1.He didn’t come ______ he was busy with his work.
A. because B. because of C. as for
2.We didn’t go out ______ the heavy snow.A. because B. because of C. since
3.______ you are tired, you can have a rest. A. Since B. Because of C. For
4.Why didn’t you attend the meeting ______ I was ill.
A. Because B. As C. Since
5.The flight was delayed ______ the thick fog.
A. as B. because C. because of
A
B
A
A
C
习题四：句型改写
1.Because it was rainy, we stayed at home.
= We stayed at home ________ ________ the rain.
2.Since he was ill, he didn’t come to school.
= ________ he was ill, he didn’t come to school.
3.She was sad because she failed the exam.
= She was sad ________ ________ her failure.
4.As the weather was bad, we didn’t go out.
= ________ ________ the bad weather, we didn’t go out.
5.He didn’t go because he was afraid.
= He didn’t go ________ ________ his fear.
because of
Because
because of
Because of
because of
习题五：用 because / as / since 合并句子
1.I didn’t go out. It was raining heavily.
2.Everyone is here. We can start our class.
3.It was too late. We had to go home at once.
4.He was ill. He didn’t take part in the sports meeting.
5.You don’t like this plan. I will change it.
I didn’t go out because it was raining heavily.
Since everyone is here, we can start our class.
As it was too late, we had to go home at once.
Because he was ill, he didn’t take part in the sports meeting.
Since you don’t like this plan, I will change it.
重点总结一
原因状语从句由 because / as / since 引导。
because 语气最强，用于回答 why。
as / since 语气较弱，多用于句首表已知原因。
because 后接句子，because of 后接名词短语。
从句句首加逗号，句末不加逗号。
重点总结二
解题先看后面成分：是句子用连词，是名词用 because of。
回答 why 只能用 because。
已知事实、显而易见的原因常用 as / since。
同义改写是考试高频题型。
规范使用标点，避免常见错误。
教学课件
Unit8语法专项—— 原因状语从句
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