在水平面内自由转动的小磁针，静止后总是一端指______，一端指______，这表明磁体具有______性，我国古代四大发明之一______就是依据这一原理制成的．
由于地球是个大磁体，且地磁北极在地理南极附近，地磁南极在地理的北极附近，所以在水平面内自由转动的小磁针，静止后由于同名磁极相互排斥，异名磁极相互吸引，则小磁针总是一端指南，一端指北，使磁体有了指向性，这也是我国四大发明之一：指南针的原理．
故本题答案为：南；北；指向；指南针．
| 口语运用, 根据所给情景选择最佳答案。 |
| 1. When your friend wants you to help him, he may say " ". |
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| A. Can I help you? B. Thank you for your help. C. Could you help me? D. You're welcome. |
| 2. If you meet a foreigner in the street, you can talk to him like " ". |
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| A. Hi! What's your name? B. Could I ask you a question? C. It's fine today, isn't it? D. Did you have the meal? |
| 3. Li Ming asks you "What do you think of the movie?", how can you answer? |
[ ] |
| A. I don't know. B. Don't ask me. C. I think so. D. I enjoy it a lot. |
| 4. When someone asks you the way to the train station, you should say " ". |
[ ] |
| A. Thank you. B. I'm afraid not. C. Sorry, please ask that policeman. D.You're unlucky, I don't know. |
| 5. If someone asks "What rules do you have at home?", you may answer " ". |
[ ] |
| A. I often watch TV. B. I'm not allowed to go out on school nights. C. I don't like to stay at home. D. It's a good question. |