Unit 5 单元语法专练- 2025-2026学年沪教版 英语八年级下册

沪教8下第五单元语法专练 It作形式主语与enough用法知识点讲解及配套练习 第一部分：It作形式主语知识点讲解 一、什么是形式主语？ 在英语中，当不定式（短语）、动名词（短语）或从句作主语时，为了避免句子头重脚轻，常用it作为形式主语放在句首，而把真正的主语放在句末。 基本结构：It + be + 形容词/名词 + 真正的主语（不定式/动名词/从句） 例如： To learn English well is important. → It is important to learn English well. That he will come is certain. → It is certain that he will come. 二、It作形式主语的常见句型 1. It + be + 形容词 + (for/of sb) + to do sth 这是最常用的句型，用于评价某事或某人的行为。 （1）It + be + 形容词 + to do sth 表示“做某事是……的”。这类形容词常见的有：important, necessary, possible, impossible, easy, difficult, hard, dangerous, useful等。 It is important to learn English well. （学好英语很重要。） It is dangerous to play with fire. （玩火很危险。） （2）It + be + 形容词 + for sb + to do sth 用for引出动词不定式的逻辑主语，表示“对某人来说做某事是……的”。这类形容词通常修饰事物，如：easy, difficult, hard, important, necessary, possible, impossible等。 It is easy for me to speak English. （对我来说说英语很容易。） It was difficult for him to finish the work. （对他来说完成这项工作很难。） （3）It + be + 形容词 + of sb + to do sth 用of引出动词不定式的逻辑主语，表示“某人做某事是……的”。这类形容词通常修饰人的品质或性格，如：kind, nice, good, clever, wise, foolish, stupid, silly, careless, polite, impolite, rude等。 It is kind of you to help me. （你帮助我真是太好了。） It was foolish of him to make such a mistake. （他犯这样的错误真愚蠢。） 辨析：for sb与of sb的区别 使用for时，形容词修饰的是“to do sth”这件事，不能改为“sb is + 形容词”。如：It is important for us to study. 不能说 We are important to study. 使用of时，形容词修饰的是“sb”的品质，可以改为“sb is + 形容词 + to do”。如：It is kind of you to help. → You are kind to help. 2. It + be + 名词 + to do sth / that从句 名词常见的有：a pity, a shame, a fact, a good idea, a pleasure, a wonder等。 It is a pity to waste time. （浪费时间真可惜。） It is a good idea to plant more trees. （种更多树是个好主意。） It is a fact that the earth is round. （地球是圆的是事实。） 3. It + be + 形容词 + that从句 这类形容词常见的有：clear, obvious, true, certain, likely, important, necessary, strange等。在important, necessary等形容词后的that从句常用“should + 动词原形”的虚拟语气。 It is clear that he is wrong. （很明显他错了。） It is important that we (should) protect the environment. （我们应当保护环境很重要。） 4. It + 不及物动词 + that从句 这类动词常见的有：seem, appear, happen, turn out, follow等。 It seems that he is ill. （他似乎病了。） It happened that I was not there. （碰巧我当时不在。） 5. It + be + 过去分词 + that从句 这类过去分词常见的有：said, reported, believed, known, thought, suggested, expected等。常译为“据说/据报道/人们相信……”。 It is said that he will come. （据说他会来。） It is reported that a new bridge will be built. （据报道将建一座新桥。） 6. It + be + no use/good + doing sth 这种句型中真正的主语是动名词短语，常用于口语中。 It is no use crying over spilt milk. （覆水难收/为洒了的牛奶哭泣没用。） It is no good smoking. （吸烟没好处。） It is a waste of time playing computer games. （玩电脑游戏是浪费时间。） 三、It作形式主语的注意事项 1. 形式主语it不可省略，不能直接用不定式或从句开头（除少数情况外）。 正确：It is important to study hard. 错误：Is important to study hard. 2. 真正的主语可以是：不定式短语、动名词短语、that从句、wh从句。 It doesn't matter where we go. （我们去哪没关系。） It is unknown whether he will come. （他是否来还不清楚。） 3. It作形式主语与强调句型的区别 It作形式主语：It + be + 表语 + 真正主语（可还原） It is important to learn English. （真正主语是to learn English） 还原：To learn English is important. 强调句型：It + be + 被强调部分 + that/who + 其他（去掉It be that后句子仍完整） It is English that I learn. （我学的是英语。——强调English） 去掉It is that后：I learn English. 句子完整。 第二部分：enough用法知识点讲解 一、enough的词性 enough可以作形容词、副词，也可以作代词。 二、enough作形容词 1. 位置：enough修饰名词时，放在名词前面。 enough + 名词 We have enough time to finish the work. （我们有足够的时间完成工作。） There aren't enough chairs for everyone. （椅子不够所有人坐。） 2. 用法：表示“足够的，充分的”，修饰可数名词复数或不可数名词。 三、enough作副词 1. 位置：enough修饰形容词或副词时，放在形容词或副词的后面。 形容词/副词 + enough He is old enough to go to school. （他够上学的年龄了。） She didn't run fast enough to catch the bus. （她跑得不够快，没赶上公交车。） 2. 常见结构：形容词/副词 + enough + to do sth 表示“足够……可以做某事” The boy is tall enough to reach the apple. （这个男孩够高，能够到苹果。） Are you warm enough in such a thin coat? （穿这么薄的衣服你够暖和吗？） 四、enough作代词 用法：enough可以单独使用，作主语或宾语，表示“足够的东西/数量”。 Enough has been said. （说得已经够多了。） I've had enough. （我受够了/我吃饱了。） 五、enough的常用句型 1. enough for sb/sth The food is enough for three people. （食物够三个人吃。） 2. enough to do He is brave enough to face the danger. （他够勇敢，能面对危险。） 3. not + 形容词/副词 + enough to do She is not old enough to drive. （她不够年龄开车。） 4. too...to... 与 enough to 的转换 He is too young to go to school. （他太小了不能上学。） = He is not old enough to go to school. （他不够年龄上学。） The box is too heavy for me to carry. （这个箱子太重了我搬不动。） = The box is not light enough for me to carry. （这个箱子不够轻，我搬不动。） 六、enough的位置口诀 “名前形副后”——修饰名词放前面，修饰形容词/副词放后面。 七、注意事项 1. enough修饰名词时，如果有形容词修饰名词，enough仍然放在形容词前面。 We have enough fresh water. （我们有足够的淡水。） 2. cannot...enough 表示“再……也不为过” You cannot be careful enough. （你再小心也不为过。） 第三部分：It作形式主语专项练习 一、单项选择（共8题） 1. ______ is important to learn English well. A. This B. That C. It D. What 2. It is very kind ______ you to help me with my homework. A. for B. of C. to D. with 3. It is difficult ______ him to finish the work in such a short time. A. for B. of C. to D. with 4. ______ is no use crying over spilt milk. A. This B. That C. It D. There 5. It is a pity ______ you can't come to the party. A. which B. that C. what D. when 6. It ______ that he has passed the exam. A. says B. said C. is said D. was said 7. It is important that everyone ______ the rules. A. follow B. follows C. following D. to follow 8. ______ seemed that he knew the truth. A. He B. It C. That D. This 二、用for或of填空（共5题） 1. It is necessary ______ us to practice English every day. 2. It was foolish ______ him to make such a mistake. 3. It is impossible ______ me to finish the work alone. 4. It was nice ______ you to help the old man. 5. It is important ______ children to eat healthy food. 三、句型转换（共5题） 1. To get up early is good for health. → ______ ______ good for health ______ ______ ______ early. 2. That he will succeed is certain. → ______ ______ certain ______ ______ ______ succeed. 3. You are very kind to help me. → ______ very kind ______ you ______ ______ me. 4. People say that he is a good teacher. → ______ ______ ______ that he is a good teacher. 5. Playing computer games too much is no use. → ______ is no use ______ computer games too much. 第四部分：enough用法专项练习 一、单项选择（共8题） 1. The boy is ______ to go to school. A. enough old B. old enough C. enough older D. older enough 2. We don't have ______ time to finish the work. A. enough B. too much C. many D. a lot 3. She is not ______ to take the job. A. enough experienced B. experienced enough C. enough experience D. experience enough 4. There are ______ chairs for everyone. A. not enough B. enough not C. no enough D. not too 5. The box is ______ heavy for the boy to carry. A. too B. enough C. so D. very 6. He ran ______ to catch the bus. A. fast enough B. enough fast C. too fast D. fast too 7. We have ______ money to buy a new car. A. too many B. enough C. many D. a few 8. You cannot be ______ careful when crossing the street. A. very B. too C. so D. enough 二、根据汉语提示完成句子（共5题） 1. 他够聪明，能解出这道题。 He is ______ ______ ______ work out the problem. 2. 我们没有足够的水喝。 We don't have ______ ______ ______ drink. 3. 她跑得不够快，没赶上火车。 She didn't run ______ ______ ______ catch the train. 4. 这个房间足够大，能容纳五十个人。 The room is ______ ______ ______ hold fifty people. 5. 他不够年龄开车。 He is ______ ______ ______ drive. 三、句型转换（共5题） 1. He is too young to join the army. → He is ______ ______ ______ ______ join the army. 2. The water is too hot to drink. → The water is ______ ______ ______ ______ drink. 3. She is clever enough to solve the problem. → She is ______ clever ______ she can solve the problem. （用so...that改写） 4. There are enough books for everyone. → There are ______ ______ books ______ everyone can have one. （用so many...that改写） 5. He didn't run fast enough to catch the thief. → He ran ______ ______ ______ catch the thief. （用too...to改写） 第五部分：答案与解析 一、It作形式主语答案与解析 （一）单项选择 1. C 解析：it作形式主语，真正的主语是to learn English well。其他选项不能作形式主语。 2. B 解析：kind是描述人的品质的形容词，用of sb。of结构可转换为：You are kind to help me. 3. A 解析：difficult是描述事物（完成工作这件事）的形容词，用for sb。 4. C 解析：it作形式主语，真正主语是动名词短语crying over spilt milk。It is no use doing是固定句型。 5. B 解析：that引导主语从句，it是形式主语，真正的主语是that you can't come to the party。 6. C 解析：It is said that... 意为“据说……”，是被动语态的常用句型。 7. A 解析：在It is important that...句型中，that从句常用虚拟语气，即should + 动词原形，should可以省略，所以填follow。 8. B 解析：It seemed that... 意为“似乎……”，it作形式主语。 （二）用for或of填空 1. for（necessary修饰事物，用for） 2. of（foolish描述人的品质，用of） 3. for（impossible修饰事物，用for） 4. of（nice描述人的品质，用of） 5. for（important修饰事物，用for） （三）句型转换 1. It is; to get up It is good for health to get up early. 2. It is; that he will It is certain that he will succeed. 3. It is; of; to help It is very kind of you to help me. 4. It is said It is said that he is a good teacher. 5. It; playing It is no use playing computer games too much. 二、enough用法答案与解析 （一）单项选择 1. B 解析：enough修饰形容词old要放在后面，old enough。 2. A 解析：time是不可数名词，用enough修饰，放在前面。 3. B 解析：experienced是形容词，enough放在后面。 4. A 解析：enough修饰名词chairs，放在前面，否定用not enough。 5. A 解析：too...to... 结构，表示“太……而不能……”。 6. A 解析：fast是副词，enough修饰副词要放在后面。 7. B 解析：money是不可数名词，用enough修饰。 8. B 解析：cannot be too 再……也不为过 （二）根据汉语提示完成句子 1. clever enough to He is clever enough to work out the problem. 2. enough water to We don't have enough water to drink. 3. fast enough to She didn't run fast enough to catch the train. 4. big enough to The room is big enough to hold fifty people. 5. not old enough to He is not old enough to drive. （三）句型转换 1. not old enough to He is not old enough to join the army. 2. not cool enough to The water is not cool enough to drink. （注意：too hot对应not cool） 或 The water is not cold enough to drink. 3. so; that She is so clever that she can solve the problem. 4. so many; that There are so many books that everyone can have one. 5. too slowly to He ran too slowly to catch the thief. （注意：fast enough的反义是too slow，但这里原句是否定，改写时注意对应） 学科网（北京）股份有限公司 $