原因状语从句because since as-2025-2026学年八年级英语下册语法重难点精讲（教科版五四制）

八下外研版 【语法专版】 原因状语从句精讲 语法专版 【语法专题】原因状语从句专项突破 初中外研版八年级下册 语法精讲 语法概述：原因状语从句(because,since,as)=用于说明主句动作或情况发生原因的从句，由 because,since,as引导，在句中作状语。 一、 重难点讲解 重难点-：because,since,as的语气强弱及适用场景讲解： because语气最强，用于回答why引导的问句，强调直接原因，可位于句首或句末，位于句末时常 用逗号与主句隔开。 Since和as语气较弱，多表示已知的、显然的原因，一般位于句首，since稍正式，as更口语化。 He didn't go to school because he was ill.(直接原因，回答why) Since everyone is here,.let's start the meeting.(已知原因，句首) As it was raining,we stayed at home..(显而易见的原因，句首) 真题再现： 1.(2024山东烟台期中，外研版)一Why did you late for class this morning?一_I missed the early bus. A.Since B.As C.Because D.For 答案：C解析：问句用why提问，回答直接原因用because。 2.(2023江苏苏州月考，外研版)_you are free today,you can help me with my English A.Because B.Since C.As D.For 答案：B解析：表示已知的原因“既然你今天有空”，用snce更正式且符合语境。 1 八下外研版 【语法专版】 原因状语从句精讲 重难点二：because与so的并用禁忌讲解： because和so不能同时出现在一个句子中，二者只能用其一。because引导原因状语从句，so引导 结果状语从句，二者在逻辑上已形成因果关系，无需重复使用。 Because he is tired,he wants to rest..（正确) He is tired,so he wants to rest.(正确) Because he is tired,so he wants to rest.(错误) 真题再现： l.(2024河北石家庄期末，外研版)_it was cold outside,_we stayed indoors, A.Because;so B.Because;/ C./;because D.So;because 答案：B解析：because和so不能同时使用，根据句意“因为外面冷，所以我们待在室内”， 用because引导原因，主句前不加so。 2.(2023 河南郑州期中，外研版)He didn't buy the book he had no money. A.so B.because C.and D.but 答案：B 解析：句意为“他没买那本书，因为他没钱”，表示原因用because,且不能与so 连用。 重难点三：原因状语从句的位置及标点符号讲解： because引导的原因状语从句可位于主句前或主句后。位于主句前时，从句后用逗号：位于主句后 时，一般不用逗号。 Since和as引导的原因状语从句通常位于主句前，从句后常用逗号。 Because she likes music,she often goes to concerts.(从句在前，用逗号) She often goes to concerts because she likes music..(从句在后，不用逗号) As the weather is fine,.we will go for a walk.(as从句在前，用逗号) 真题再现： 1.(2024辽宁沈阳月考，外研版)she is very young,she knows a lot of things. A.Because B.Though C.As D.So 答案：C解析：从句“她很年轻”位于主句前，且表示已知原因，用s引导，符合语法规 则。 2.(2023山东威海期末，外研版)He couldn’t sleep well_he was too excited. 2 八下外研版 【语法专版】 原因状语从句精讲 A.because B.so C.and D.but 答案：A解析：从句“他太兴奋”位于主句后，说明睡不着的原因，用because且无需逗号。 易错点综合演练 L单项选择（直击重难点） 1.-Why didn't Peter join the hiking trip yesterday? -he had a bad cold and needed to rest. A.Since B.As C.Because D.For 2.you have finished your homework,you can watch TV for half an hour. A.Because B.Since C.As D.For 3.it rained heavily,we still arrived at the station on time. A.Because B.Since C.As D.Though 4.He was late for school he missed the first bus. A.so B.because C.and D.but Ⅱ.用所给词的适当形式填空（强化句型结构） 1.(because)he is very friendly,everyone likes to make friends with him. 2.She didn't go to the park(so)it was raining. 3.(since)you are here,you can help me carry the box. 4.He was tired,(so)he went to bed early. 3 八下外研版 【语法专版】 原因状语从句精讲 Ⅲ.短文填空（综合运用原因状语从句） 用because,since,as或so填空，使短文完整通顺。 Tom couldn't go to the party last night 1.he had to study for an exam.2.his friends knew he was busy,they didn't call him.Mary wanted to go to the party,3.she had a headache.4.it was a pity,they all understood. V.按要求改写句子（巩固否定、疑问句式） 1.He stayed at home because he was ill.(对划线部分提问) 2.Because it was late,we had to take a taxi..(改为同义句) 3.He is tired,so he wants to sleep.(改为复合句) 4.Because she likes reading,she has many books..(改为简单句) 参考答案 I.单项选择：1.C2B3D4.B Ⅱ.用所给词的适当形式填空：1.Because 2.because 3.Since 4.so 皿短文填空： 1.because 2.Since 3.because 4.As V.按要求改写句子： 1.Why did he stay at home? 2.It was late,so we had to take a taxi. 3.Because he is tired,he wants to sleep. 4.She likes reading,so she has many books 4