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    People in many countries are learning English.Some of them are small children. Others are teenagers. Many are adults. Some learn at school, others learn by themselves. A few people learn English by hearing the language over the radio, on TV or in films. As we know, it's hard to learn a foreign language well. One must work hard to learn another language. Because we can't use it often. But if you have right ways to learn English, it's a piece of cake.

    Why do all these people want to learn English?It is difficult to answer this question. Many boys and girls learn English at school because it is one of their subjects required (要求) for study. They study their own language, math and English. Some people learn it because it is useful for their work. Many people learn English for their higher studies,because at colleges or universities some of their books are in English. Some people learn English because they want to read newspapers or magazines in English.

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Ⅰ：C、N、O、Al、Si、Cu是常见的六种元素．

（1）Si位于元素周期表第 ____周期第 ____　族．

（2）N的基态原子核外电子排布式为　 ____　；Cu的基态原子最外层有　 ____　个电子．

（3）用“＞”或“＜”填空：

Ⅱ：

（4）H₂O₂的电子式　 ____　．

（5）镁燃烧不能用CO₂灭火，用化学方程式表示其理由 ____　．

（6）在AgCl沉淀中加入KBr溶液，白色沉淀转化为淡黄色沉淀，写出反应的离子方程式 ____

（7）完成以下氧化还原反应的离子方程式：

 ____MnO₄^﹣+ ____C₂O₄^2﹣+ ____= ____Mn²⁺+ ____CO₂↑+ ____