Unit4语法讲解及习题：for + clause to show reason（for引导原因状语从句） 2025-2026学年沪外教版八年级英语下册

沪外教英语八下Unit4语法讲解及习题 for + clause to show reason（for引导原因状语从句） 一、语法详细讲解 1. 核心定义 for + 从句 用于引导原因状语从句，含义为“因为；由于”，和 because 语义基本一致，用于补充说明主句动作/情况的理由。 2. 基本结构 主句（完整句子）, for + 原因从句（完整句子） 注意：for 前通常加逗号，且 for 引导的从句不能放在句首，只能放在主句后。 例句： a. We should reduce plastic use, for it harms sea animals. 译：我们应该减少塑料使用，因为它会伤害海洋动物。 b. The river is polluted, for people throw waste into it. 译：这条河被污染了，因为人们往里面扔垃圾。 3. for vs because 核心区别（考试必考点） 维度 for because 语气 较正式、书面化，补充说明理由（语气弱） 更口语化、常用，直接强调原因（语气强） 位置 只能放在主句后，前面必须加逗号 可放在主句前/后，放句首时后加逗号 用法场景 用于书面写作、正式说明（如环保倡议、规则介绍） 日常对话、普通写作均可 例句 We must save water, for water is limited. Because water is limited, we must save it. / We must save water because water is limited. 4. 关键使用规则 for 后必须接完整句子（主语+谓语），不能接名词/短语（接名词用 because of）。 错误：We should recycle, for the environment. 正确：We should recycle, for it can protect the environment. for 引导的从句不能回答 "Why...?"，回答 Why 必须用 because。 错误：—Why do you save water? —For water is limited. 正确：—Why do you save water? —Because water is limited. 时态一致：主句和从句时态保持一致（同现在时/过去时等）。 过去时：Thomas became a green volunteer, for he cared about the earth. 现在时：We take short showers, for it helps save water. 2、 习题 题型1：单项选择 1. We should plant more trees, ___________ they can take in CO₂. A. for B. because of C. but D. so 2. The air is getting cleaner, ___________ people use fewer cars now. A. for B. because C. A and B D. none 3. We mustn’t pick wild plants, ___________ some are endangered. A. for B. because C. A and B D. so 4. We should turn off lights when leaving, ___________ it saves energy. A. for B. because of C. but D. so 5. Many animals are in danger, ___________ their homes are destroyed. A. for B. because C. A and B D. but 6. We should use reusable bags, ___________ plastic bags pollute the sea. A. for B. because C. A and B D. so 7. He never takes shortcuts in the park, ___________ it hurts small plants. A. for B. because C. A and B D. but 8. We should sort rubbish, ___________ it can be recycled easily. A. for B. because of C. but D. so 9. The river is dirty, ___________ people throw rubbish into it every day. A. for B. because C. A and B D. so 10. We should save paper, ___________ fewer trees will be cut down. A. for B. because C. A and B D. but 题型2：用 for / because 完成句子 1. We should use both sides of the paper, ___________ we can cut down fewer trees. 2. We should pick up the trash on the street, ___________ it is our responsibility to keep our environment clean. 3. We shouldn’t leave the water running, ___________ it is important to protect water resources. 4. We should ride bikes more often instead of driving cars, ___________ it is helpful to reduce greenhouse gas. 5. Never pick plants or collect rocks, ___________ some are endangered. 6. Never try to touch wild animals, ___________ many may be endangered and it’s also against the law! 7. Human’s food is not good for wild animals, ___________ too much of it can make animals dependent on humans. 8. Never take shortcuts, ___________ they can lead you into dangerous places. 题型3：句子匹配与合并 将左右句子用 for 合并，注意加逗号： 1. We should take short showers. a. it can save a lot of water. 2. We should sort rubbish. b. it can reduce pollution. 3. We mustn’t feed wild animals. c. it can protect animals’ natural habits. 4. We should walk to school. d. it can cut down air pollution. 5. We should use energy-saving bulbs. e. it can help save electricity. → 1. _____________________________________________________________________ → 2. _____________________________________________________________________ → 3. _____________________________________________________________________ → 4. _____________________________________________________________________ → 5. _____________________________________________________________________ 题型4：短文填空 用 for 或 because 完成环保短文（注意格式）： Protecting the earth is our duty. 1.___________ we have only one earth, we must take good care of it. We should reduce plastic use, 2.___________ plastic bags are harmful to sea animals. We should plant more trees, 3.___________ trees can clean the air. We mustn’t waste water, 4.___________ fresh water is limited. We should take public transport, 5.___________ it can reduce car emissions. We should recycle old things, 6.___________ it can save resources. We mustn’t pick wild flowers, 7.___________ they are part of the ecosystem. We should turn off taps tightly, 8.___________ dripping water wastes a lot. We should use cloth bags, 9.___________ plastic bags take hundreds of years to break down. We should teach kids to protect nature, 10.___________ they are the future of the earth. 三、答案与解析 题型1：单项选择 1. A — for 引导补充原因，符合逗号+从句结构；because 也可，此处选A更贴合书面用法。 2. C — for 和 because 均可表原因，语义一致，故选C。 3. C — for 和 because 均可说明“植物濒危”的理由，故选C。 4. A — for 补充“节约能源”的理由，符合逗号+从句；because of 后接名词，排除。 5. C — for 和 because 均可说明“家园被毁”的原因，故选C。 6. C — for 和 because 均可说明“塑料袋污染海洋”的理由，故选C。 7. C — for 和 because 均可说明“伤害植物”的原因，故选C。 8. A — for 补充“便于回收”的理由，符合逗号+从句；because of 后接名词，排除。 9. C — for 和 because 均可说明“扔垃圾”的原因，故选C。 10. C — for 和 because 均可说明“少砍树”的理由，故选C。 题型2：用 for / because 完成句子 1. for / because — 补充“少砍树”的理由，两种均可。 2. for / because — 补充“保持环境清洁”的责任，两种均可。 3. for / because — 补充“保护水资源”的重要性，两种均可。 4. for / because — 补充“减少温室气体”的作用，两种均可。 5. for / because — 补充“植物濒危”的原因，两种均可。 6. for / because — 补充“动物濒危且违法”的理由，两种均可。 7. for / because — 补充“让动物依赖人类”的后果，两种均可。 8. for / because — 补充“带来危险”的原因，两种均可。 题型3：句子匹配与合并 1. We should take short showers, for it can save a lot of water. 解析：for 引导补充原因，逗号分隔主句和从句。 2. We should sort rubbish, for it can reduce pollution. 解析：for 说明垃圾分类的环保作用。 3. We mustn’t feed wild animals, for it can protect animals’ natural habits. 解析：for 补充“不投喂野生动物”的理由。 4. We should walk to school, for it can cut down air pollution. 解析：for 说明步行上学的环保意义。 5. We should use energy-saving bulbs, for it can help save electricity. 解析：for 补充使用节能灯泡的原因。 题型4：短文填空 1. Because — 放句首强调原因，只能用 because（for 不能放句首）。 2. for / because — 主句后补充原因，两种均可。 3. for / because — 主句后补充树木的作用，两种均可。 4. for / because — 主句后补充淡水有限的事实，两种均可。 5. for / because — 主句后补充公共交通的环保作用，两种均可。 6. for / because — 主句后补充回收的意义，两种均可。 7. for / because — 主句后补充野花的生态价值，两种均可。 8. for / because — 主句后补充滴水浪费的后果，两种均可。 9. for / because — 主句后补充塑料袋难降解的问题，两种均可。 10. for / because — 主句后补充孩子是未来的理由，两种均可。 ( 1 ) 学科网（北京）股份有限公司 $