已知用金属钠生成氧化钠，可用多种方法：
①4Na+O2
2Na2O
②4Na+CO22Na2O+C
③2NaNO2+6Na4Na2O+N2↑
上述三种方法中最好的是________，原因是________________________。
③产物中只有Na2O固体生成，且N2可以把周围环境中的O2排净，保护了Na2O
方法①用钠与O2直接反应，生成的Na2O将有少量发生反应2Na2O+O2
2Na2O2，即产物是Na2O和Na2O2的混合物。方法②中固体产物中既有C又有由反应Na2O+CO2Na2CO3生成的Na2CO3。方法③产物较纯净，且不易变质（有N2的保护）。
| 阅读理解。 |
| Newspapers are very important in our daily life. Many people begin their day by reading the paper. In this way they learn what is going on in the world. Sometimes, however, they didn't have the time to read the news carefully and must be pleased with a quick look at the front page. At other times they may be in such a hurry that they have time only to have a quick look at the headlines. There are newspapers to please every reader. In big cities there are many types with several different editions (版) every day. In some towns there are fewer newspapers and perhaps only one edition each day. In some places the paper is printed (印刷) weekly. Most papers have several editions, especially on Sundays when the edition is larger than usual. There are besides the front page with the most important news, the sports news, the amusement page, a business page and so on. |
| 1. People read newspapers to ______. |
[ ] |
| A. learn about the less important news B. be pleased C. learn about whatever they want D. get some information |
| 2. Reading the headlines, people can know ______. |
[ ] |
| A. what the passages are about B. what they are going to do C. about the most important news D. about sports |
| 3. In big cities newspapers are usually printed ______. |
[ ] |
| A. daily B. weekly C. monthly D. yearly |
| 4. Most papers have ______ on Sundays than usual. |
[ ] |
| A. more types B. more pages C. fewer types D. fewer pages |
| 5. If you want to see a film, you'd better read ______ in a newspaper. |
[ ] |
| A. the business page B. the front page C. the sports page D. the amusement page |