如图是铁丝在氧气中燃烧的实验，请回答下列问题．
（1）集气瓶底铺上一层细砂，其作用是______；
（2）实验中观察到的现象是______；
（3）反应的文字表达式______．
（1）铁丝在氧气中燃烧时，为了防止溅落的熔化物炸裂集气瓶底，集气瓶底铺上一层细砂或预留少量水；
（2）实验中观察到的现象是：剧烈燃烧，火星四射，生成黑色固体，放出大量的热；
（3）铁丝在氧气中燃烧生成了四氧化三铁，反应的文字表达式：铁+氧气
四氧化铁．点燃
故答为：（1）防止溅落的熔化物炸裂瓶底；
（2）剧烈燃烧，火星四射，生成黑色固体，放出大量的热；
（3）铁+氧气
四氧化铁．点燃
Now students’ English handwriting gets worse and worse. That makes their teachers feel worried. Is your English handwriting beautiful? If not, here are four steps that really work! ◆Use paper that has lines Using paper that has lines can keep you writing straight when you write English words or sentences. Those lines on the paper can help you to write words in the right size. Be sure to fill the lined space completely. And make sure those capital letters(大写字母) are written properly. ◆Slow down If your writing is hard to read, try slowing down a little. For some kids, going slower makes the handwriting clear. If you write too fast, it’s hard for you to stop where you should, and even worse, you may make more mistakes. ◆ Hold your pencil right When you hold your pencil the correct way, writing is much easier. Some kids press(按,压) down really hard when they write. That makes the handwriting not nice. Try to relax yourself and don’t hold the pencil so hard. Let your writing appear nice and clean. If you do so, people will guess you are a student with a good habit. ◆Draw more pictures Drawing can improve your handwriting. You need to use the skills to control your pencil better when you are drawing pictures. Even though you have no chance to draw at school, you can practice by yourself at home. Handwriting is very important. Imagine you are a world-famous movie star or a well-known sports player, what do you do when your fans run up to you? Give them your autographs (亲笔签名), of course！
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