Unit 4 Protecting Mother Earth-同步【语法】-for 引导原因分句-2025-2026学年沪外教版八年级下册

该初中英语讲义围绕“for引导原因分句”构建单元语法复习体系，通过对比表格系统梳理for与because的逻辑差异、位置规则、标点要求等核心要点，结合定义阐释、标准句式归纳及易错警示，清晰呈现知识脉络与重难点内在联系。 讲义亮点在于分层练习设计，基础层通过合并句子、选词填空夯实基础，提升层借助中译英、改错强化语言运用能力，拓展层结合任务型阅读与书面表达培养逻辑推断的思维品质。每个题型均配详细解析，助力不同层次学生提升，为教师精准教学与学生自主复习提供有力支持。

Unit 4 Protecting Mother Earth-同步【语法】-for 引导原因分句 【同步语法复习】 1、 语法知识点 (1) 核心定义 · for 是并列连词 用来连接两个并列分句，补充、推测主句发生的缘由，不能用来回答 why 引导的问句。 · 标准句式：主句，for + 原因分句 · 硬性规则： ① for 只能放在主句后方，绝对不能置于句首 ② for 前面必须加逗号 ③ for 连接的分句是对前文现象的补充推断，不是直接因果 (2) for VS because 重难点对比 项目 because（从属连词） for（并列连词） 逻辑 直接、内在因果，客观原因 补充说明、推测性理由，外在依据 位置 句首 / 主句后均可 只能放在主句之后 标点 放句首时，主句前加逗号；主句前不加逗号 主句和 for 之间必须加逗号 问答 可以直接回答 Why 问句 不能回答 Why 问句 使用 场景 口语、书面语通用，使用广泛 多见于正式书面英语 例句： He must be tired, for he fell asleep quickly. （推测依据：很快入睡，推断很累，用 for） He is tired because he worked all day. （直接说明劳累的根源，用 because） (3) 易错警示 （错误） For the weather is bad, we stay indoors.（for 放句首，错误） （正确）We stay indoors, for the weather is bad. （错误） We plant trees for they protect the soil.（缺少逗号，错误） （正确）We plant trees, for they protect the soil. 2、 课本习题 (1) 课本习题C1 Q1 What do the sentences after “for” mean? 答案：They provide the reason or evidence to explain the statement in the main clause. 解析：for 引导分句，为主句陈述的事实提供理由、推断依据，属于补充说明。 Q2 What are the differences between the use of “for” and “because”? 答案： 1. for 是并列连词，只能置于主句之后，前面要有逗号；because 是从属连词，位置灵活。 2. because 侧重直接因果，可以回答 why；for 侧重推测、补充理由，不可回答 why。 3. because 日常使用更加普遍；for 多用于书面文体。 (2) 课本习题C2 1 We should use both sides of the paper, (c)for we can cut down fewer trees. 句意：我们纸张双面使用，这样能够减少树木砍伐。 解析：双面用纸可以减少纸张消耗，进而减少伐木，逻辑匹配 c；严格遵循「主句，for +分句」结构。 2 We should pick up the trash on the street, (a)for it is our responsibility to keep our environment clean. 句意：我们应当捡拾街道垃圾，保持环境整洁是我们的责任。 解析：捡拾垃圾与维护环境责任对应选项 a。 3 We shouldn’t leave the water running, (d)for it is important to protect water resources. 句意：我们不应该任由水流淌，保护水资源至关重要。 解析：杜绝长流水对应水资源保护，匹配 d。 4 We should ride bikes more often instead of driving cars, (b)for it is helpful to reduce greenhouse gas. 句意：我们应当多骑自行车少开车，这有助于减少温室气体。 解析：绿色出行减少碳排放，匹配 b。 (3) 课本习题C3 · Never pick plants or collect rocks, for many may be endangered and it’s also against the law! 句意：不要采摘植物、捡拾岩石，许多物种可能濒临灭绝，并且这种行为涉嫌违法。 解析：解释禁止采摘动植物的原因，选用 b。 · Human’s food is not good for wild animals, for too much of it can make animals dependent on humans. 句意：人类食物不适合野生动物，过多投喂会让动物对人类产生依赖。 解析：对应投喂野生动物的危害，选用 c。 · Never take shortcuts, for they can lead you into dangerous places. 句意：不要抄近道，小路可能将你带入危险区域。 解析：解释禁止走捷径的安全原因，选用 a。 (4) 课本习题C4 1 I think the use of plastic bags should not be allowed, for plastic waste takes hundreds of years to break down. 句意：我认为塑料袋应当被禁用，塑料垃圾需要数百年才能降解。 解析：for 引出禁止塑料袋使用的理由，书面表达规范。 2 I think it’s a good idea, for taking short showers helps save fresh water. 句意：我认为这是个好主意，缩短淋浴时长有助于节约淡水资源。 解析：for 解释短淋浴的环保意义。 【同步语法练习】 ——基础层—— 1、 仿照示例，用 for 合并句子 要求：将两个简单句合并，使用“主句，for + 分句” 例：The lake looks dirty. Lots of waste is poured into it. → The lake looks dirty, for lots of waste is poured into it. 1. We must save energy. Fossil fuels will run out one day. 2. Stop throwing rubbish into rivers. Rubbish kills river wildlife. 3. Choose reusable cups. Disposable cups create tons of waste. 4. We should sort rubbish. It makes waste recycling much easier. 5. Don’t buy overpackaged goods. Too much packaging wastes resources. 6. We should protect wetlands. Wetlands offer home to plenty of wildlife. 2、 选词填空 （for /because） 1. ____ sea levels are rising, more coastal places face risks. 2. The birds fly south, ____ cold winter is coming. 3. We can’t cut down this ancient tree, ____ it protects the hillside. 4. He cycles to school every day ____ he wants to cut air pollution. 5. ____ many forests are destroyed, some animals lose their homes. 6. The air feels fresh, ____ heavy rain washed away the dust. ——提升层—— 1、 中译英 1. 我们应当节约用水，因为淡水资源十分有限。 2. 不要捕杀野生动物，因为它们维持着自然界的生态平衡。 3. 我们多种树木，因为树木能够阻挡风沙。 4. 尽量绿色出行，因为汽车尾气会污染空气。 5. 我们拒绝一次性塑料袋，因为它们很难降解。 2、 改错（划出错误并改正） 1. For plastic never disappears quickly, we should reduce its use. 2. We must protect wildlife for many animals are losing their homes. 3. It must be very cold outside because the lake has frozen. 4. I choose cloth bags because plastic bags pollute the ocean 5. For we pollute rivers, many fish disappear year by year. 6. We save electricity for it helps protect natural resources. ——拓展层—— 1、 任务型阅读 Green lifestyle means living in a way that does little harm to nature. Everyone can take small actions. We should choose public transport, for private cars produce plenty of harmful gas. We can also grow some plants at home, for green plants take in carbon dioxide and make fresh oxygen. We’d better repair broken things instead of throwing them away, for making new products always costs lots of energy. Besides, we should learn to share things with others. Sharing cuts waste, for fewer new goods will be needed. However, many teenagers do not realize how important green habits are. Teachers and parents should guide them patiently, for good habits formed at young ages can last a lifetime. Small acts can bring great changes to our earth. 根据短文内容，简要回答问题。 1. Why should we choose public transport? 2. What advantage do green plants have? 3. Why should we repair broken things rather than throw them away? 4. What can we do to cut waste according to the passage? 5. Why should adults guide teenagers to build green habits? 2、 书面表达 题目：Protect our living environment 写作要点： 1. 保护环境是每个人的责任 2. 列举两条可行做法 3. 使用 for 说明理由（至少两处） 4. 抒发个人观点 5. 80-100词左右 参考答案和解析 ——基础层—— 一、 仿照示例，用 for 合并句子 1. → Stop throwing rubbish into rivers, for rubbish kills river wildlife. 句意：不要向河中丢弃垃圾，垃圾会夺去水生生物的生命。 解析：祈使句作主句，for 置于主句后并用逗号隔开，引出这条禁令背后补充性的理由。 2. → Choose reusable cups, for disposable cups create tons of waste. 句意：选择可重复使用水杯，一次性杯子会产生海量垃圾。 解析：祈使句作为主句，for 前添加逗号，用来解释提倡使用环保水杯的推断依据。 3. → We should sort rubbish, for it makes waste recycling much easier. 句意：我们应当垃圾分类，这会让垃圾回收工作更加便利。 解析：陈述句作主句，遵循「主句，for + 分句」结构，for 引出支撑主句观点的补充理由。 4. → Don’t buy overpackaged goods, for too much packaging wastes resources. 句意：不要购买过度包装商品，过多包装会浪费资源。 解析：否定祈使句作主句，for 前必须加逗号，用来解释不选购过度包装商品的原因。 5. → We should protect wetlands, for wetlands offer home to plenty of wildlife. 句意：我们应当保护湿地，湿地是大量野生动植物的家园。 解析：陈述句作主句，逗号置于 for 之前，for 引出建议保护湿地的事实依据，属于书面补充说明。 二、 选词填空 （for /because） 1. 答案：Because 句意：海平面不断上升，更多沿海地区面临威胁。 解析：连词位于句首，只能使用 because；for 不能置于句首。 2. 答案：for 句意：鸟儿向南迁徙，寒冷的冬季即将到来。 解析：根据候鸟迁徙推测冬季来临，属于推测依据，主句后逗号隔开，选用 for。 3. 答案：for 句意：我们不能砍伐这棵古树，它守护着这片山坡。 解析：主句后置理由，逗号隔开，补充说明。 4. 答案：because 句意：他每天骑车上学，因为他想要减少空气污染。 解析：直接说明主观动机，内在因果，可用 because。 5. 答案：Because 句意：大量森林遭到破坏，一些动物失去栖息地。 解析：连词放在句首，只能用 because。 6. 答案：for 句意：空气十分清新，大雨冲刷走了空气中的尘埃。 解析：由空气清新推测此前下过大雨，属于推测依据。 ——提升层—— 一、 中译英 1. → We should save fresh water, for fresh water resources are very limited. 句意：我们应当节约用水，淡水资源十分有限。 解析：陈述句为主句，for 前添加逗号，for 引出支撑节水倡议的客观依据，符合书面语中 for 表补充理由的用法。 2. → Don’t hunt wild animals, for they keep the balance of nature. 句意：不要捕杀野生动物，它们维持着自然界的生态平衡。 解析：否定祈使句作主句，遵循「主句，for + 分句」格式，for 用来解释禁令背后的理由。 3. → We should plant more trees, for trees can stop wind and sand. 句意：我们应当种植更多树木，树木能够阻挡风沙。 解析：陈述句作主句，逗号隔开 for，for 引出提倡植树的事实依据。 4. → Try to travel in green ways, for car waste gas will pollute the air. 句意：尽量绿色出行，汽车尾气会污染空气。 解析：祈使句作主句，for 前加逗号，补充说明倡导绿色出行的缘由。 5. → We refuse disposable plastic bags, for they are hard to break down. 句意：我们拒绝一次性塑料袋，它们很难降解。 解析：陈述句作主句，使用规范句式结构，for 引出拒绝塑料袋的重要原因。 二、 改错（划出错误并改正） 1. F 改正：We should reduce its use, for plastic never disappears quickly. 句意：我们应当减少塑料使用，塑料很难快速降解。 解析：for 引导原因分句禁止放在句首。 2. F 改正：We must protect wildlife, for many animals are losing their homes. 句意：我们必须保护野生动物，许多动物正在失去家园。 解析：for 和主句之间缺少逗号。 3. F 改正：It must be very cold outside, for the lake has frozen. 句意：外面一定很冷，湖面已经结冰了。 解析：通过湖面结冰推测气温低，属于推测依据，适合用 for。 4. T 句意：我选择布袋，塑料袋会污染海洋。 解析：because 放在主句后，描述直接因果，用法无误。 5. F 改正：Many fish disappear year by year, for we pollute rivers. 句意：鱼类逐年消失，因为人类污染河流。 解析：for 不可置于句首。 6. F 改正：We save electricity, for it helps protect natural resources. 句意：我们节约用电，这有助于保护自然资源。 解析：主句与 for 之间缺少逗号。 ——拓展层—— 一、 任务型阅读 1. 答案：For private cars produce plenty of harmful gas. 句意：因为私家车会排放大量有害气体。 解析：定位文中 “We should choose public transport, for private cars produce plenty of harmful gas.”，本题考查 for 引导并列分句表补充理由；回答 why 问句时，可以直接使用 for 引出依据。 2. 答案：Green plants take in carbon dioxide and make fresh oxygen. 句意：绿植可以吸收二氧化碳，制造新鲜氧气。 解析：定位原文 “We can also grow some plants at home, for green plants take in carbon dioxide and make fresh oxygen.”，提取 for 分句内绿植作用的核心信息作答。 3. 答案：For making new products always costs lots of energy. 句意：制造新产品通常会消耗大量能源。 解析：依据 “We’d better repair broken things instead of throwing them away, for making new products always costs lots of energy.” 作答。 4. 答案：We can share things with other people. 句意：我们可以和他人共享物品。 解析：定位 “Sharing cuts waste, for fewer new goods will be needed.”，前半句点明共享物品能够减少浪费，据此提炼答案。 5. 答案：For good habits formed at young ages can last a lifetime. 句意：年少养成的好习惯能够持续一生。 解析：锁定 “Teachers and parents should guide them patiently, for good habits formed at young ages can last a lifetime.”。 二、 书面表达 参考范文 Protect our living environment It is everyone’s duty to protect our living environment. First, we should plant more trees around us, for trees can clean the air and stop soil from being washed away. Second, we ought to avoid disposable products in daily life, for they create mountains of rubbish and take many years to break down. We should also encourage family and friends to stick to green lifestyles. Never wait until environmental problems become worse. Let’s take small actions right now, for the earth is the only warm home for all living things. 学科网（北京）股份有限公司 $