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2026春季新版八年级下册外研版Unit 4 Helping out 语法讲义
Grammar：情态动词精讲精练
当我们想表达可能发生某事以及某人可能做某事时，可以用may / might表示。
例如:
Bring a map because you may want to travel around. 带张地图，因为你可能想四处转转。
There may be a few showers, so bring an umbrella with you. 可能会有阵雨，所以随身带把伞吧。
在表示现在或将来的可能情况时，might表示的可能性比may表示的可能性要小一些。
例如:Take your swimming clothes because you might want to go swimming in the sea.
带上游泳衣吧，说不定你想到海里游泳呢。
情态动词can和could除了表示“能够，可以”等意义之外，还可以表示对现在或将来的推测，意为“会，可能”。但can表示推测时，往往用于否定句和疑问句。用于疑问句时，can比could表示的可能性要大; 用于否定句时, cannot (can't) 表示“不可能”。
例如:You can't be serious! 你不是认真的吧!
could则可用于肯定句、否定句和疑问句。在以下例句中, can和could均表示“可能”:
He could be in pain. 他可能很疼。
That could be harmful! 那可能有害!
Can / Could this be true 这有可能是真的吗
情态动词must也可以表示猜测，意为“一定，肯定”，通常只用于肯定句。例如:
Betty, you must know! Betty, 你肯定知道!
请仔细对比下面一组句子:
-Who sent the present Can it be your brother
是谁送来的礼物啊？会是你哥哥吗 (询问可能性)
-It must be your brother. I saw him in your room just now.
肯定是你哥哥,我刚才看见他在你的房间里。(语气强烈, 表示非常肯定)
-It can't be my brother. He is still in France.
不可能是我哥哥, 他还在法国呢。(表示不可能)
外研版八年级下册Unit 4 情态动词专项练习
一、单项选择
( ) 1. —Where is Tom
—He ______ in the library. He likes reading there after school.
A. must be B. can't be C. might be D. need be
( ) 2. —Is that Mr. Li over there
—It ______ be him. He has gone to Beijing on business.
A. mustn't B. can't C. may not D. shouldn't
( ) 3. The light is on in her room. She ______ be at home now.
A. can B. must C. can't D. might
( ) 4. —______ the story be true
—No, it can't be true. It sounds impossible.
A. Can B. Must C. Need D. Should
( ) 5. You ______ bring your camera, because you ______ want to take photos of the beautiful park.
A. can; must B. must; can C. may; might D. might; must
( ) 6. —Who is knocking at the door
—It ______ be my dad. He said he would come back this afternoon.
A. can B. must C. can't D. might
( ) 7. This medicine ______ be harmful if you take too much. You must follow the doctor's advice.
A. can B. must C. can't D. need
( ) 8. —The classroom is empty. Where are the students
—They ______ be in the playground. They often play basketball there at this time.
A. must B. can't C. might D. need
( ) 9. —Look! The girl in red ______ be Lucy.
—No, it ______ be her. Lucy has gone to Shanghai.
A. must; can't B. can; mustn't C. may; needn't D. can't; must
( ) 10. Take an umbrella with you. It ______ rain this afternoon. The weather report says there is a small chance of rain.
A. must B. can C. might D. can't
二、用 must, might, could, can't 填空
1. The phone is ringing, but no one answers. They ______ be at home.
2. The ground is all wet. It ______ have rained last night.
3. She hasn't contacted us for three days. She ______ be in trouble, but we're not sure.
4. That ______ be my textbook. Mine is in my schoolbag.
5. You ______ be tired after working for ten hours without a rest.
6. —Is that the new student
—It ______ be her. I saw her name on the class list just now.
7. The noise next door ______ be from the children playing. They usually play there at this time.
8. He ______ be in the office. The light is off and the door is locked.
9. —______ this be the right way to the station
—I'm not sure. We can ask the policeman over there.
10. Don't worry. It ______ be a serious problem. It's probably just a small mistake.
三、句型转换（保持句意不变）
1. I am sure that he is in the classroom now.
He ______ ______ in the classroom now.
2. It is impossible that he has finished the work in such a short time.
He ______ ______ finished the work in such a short time.
3. Perhaps she will come to the party tonight.
She ______ come to the party tonight.
4. Is it possible that they are having a meeting now
______ they ______ having a meeting now
5. I'm not sure if this is the correct answer.
This ______ be the correct answer.
四、情景对话（补全对话，每空一词）
A: Look! Someone is standing at the school gate. ______ it be our new teacher
B: It ______ be her. She told me she would come at 9:00, but it's only 8:30 now.
A: Then who ______ it be
B: It ______ be your father. He said he would come to see you today.
A: No, it ______ be him. He is still in Shanghai on business.
B: Oh, it ______ be the gatekeeper. He often stands there early in the morning.
A: You're right! That must be him.
五、句子翻译（使用情态动词表推测）
1. 这本书一定是她的。上面有她的名字。
___________________________________________________
2. 他不可能在家，因为他的车不在外面。
___________________________________________________
3. 明天可能会下雨，所以你最好带把伞。
___________________________________________________
4. 这可能不是一个好主意，我们再想想吧。
___________________________________________________
5. ——那个穿蓝色衣服的女孩是谁？
——可能是我的妹妹，也可能不是，我不太确定。
___________________________________________________
___________________________________________________外研版八年级下册 Unit 4 情态动词专项练习 答案+逐题解析
一、单项选择
1. A
解析：后文说他放学后喜欢在那里看书，语气非常肯定，用must be（一定在）。
2. B
解析：他去北京出差了，所以“不可能”是他，can’t 表示否定推测“不可能”。
3. B
解析：房间灯亮着，很肯定她在家，用must。
4. A
解析：疑问句中表推测用Can（可能……吗？）。
5. C
解析：前半句“你可以带相机”，后半句“你可能想拍照”，可能性不大，用may; might。
6. B
解析：爸爸说过今天下午回来，很肯定，用must。
7. A
解析：can 用于肯定句表理论上的可能“这种药吃多可能有害”。
8. A
解析：这个时间他们常去操场打球，很肯定，用must。
9. A
解析：第一空肯定猜测用must；第二空Lucy去上海了，不可能是她，用can’t。
10. C
解析：天气预报说下雨可能性小，用might（可能，可能性较低）。
二、用 must, might, could, can't 填空
1. can’t
解析：电话响没人接，不可能在家。
2. must
解析：地面全湿了，一定昨晚下雨了。
3. might/could
解析：不确定，可能遇到麻烦。
4. can’t
解析：我的书在书包里，不可能是我的。
5. must
解析：连续工作10小时，一定很累。
6. must
解析：刚在名单上看到名字，一定是她。
7. must
解析：这个时间孩子常在这里玩，一定是他们。
8. can’t
解析：灯关着门锁了，不可能在办公室。
9. Could/Can
解析：疑问句表推测“这可能是去车站的路吗？”。
10. can’t
解析：只是小错误，不可能是严重问题。
三、句型转换
1. must be
解析：I am sure = must（肯定推测）。
2. can’t have
解析：impossible = can’t（不可能）。
3. may/might
解析：perhaps = may/might（可能）。
4. Can; be
解析：Is it possible = Can…be…。
5. might/could
解析：not sure = might/could（可能）。
四、情景对话
1. Can（疑问句表推测）
2. can’t（时间没到，不可能）
3. can（可能是谁）
4. must（爸爸说过来看你，一定是）
5. can’t（在上海出差，不可能）
6. must（门卫常站在那里，一定是）
五、句子翻译
1. This book must be hers. There is her name on it.
解析：有名字→肯定推测用must。
2. He can’t be at home because his car isn’t outside.
解析：车不在→不可能在家，用can’t。
3. It may/might rain tomorrow, so you’d better take an umbrella.
解析：可能下雨→may/might。
4. This may not be a good idea. Let’s think again.
解析：可能不是→may not。
5. —Who is the girl in blue
—It may/might be my sister. I’m not sure.
解析：不确定→may/might。

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