煤炭在锅炉内燃烧经过那几个阶段？
参考答案：
（1）干燥阶段----煤从炉膛内吸热，温度升高，水分被蒸发。
（2）挥发份析出及其燃烧阶段----水分蒸发完后，温度继续升高，挥发份随之不断析出，达到着火温度时，逸出的挥发份在煤粒表面开始燃烧。
（3）焦碳燃烧阶段----挥发份燃烧后使温度进一步升高，使煤析出挥发份后形成的焦碳开始燃烧并放出大量的热量。
（4）燃尽阶段----焦碳燃烧到一定时间后，大部分含碳物质已烧完直至燃尽。
先通读短文，然后根据短文内容，选择适当的单词填空，使短文意思完整。 In recent years, studying Chinese in China has become popular with foreigners. Some Chinese classroom manners are______ from western classroom manners. It might be a good idea to know something about these ______ you take a Chinese class. Being respectful (尊重的) Students in China respect their teachers very much. When ______ your teacher, you should always use your teacher’s surname (姓), followed by "laoshi" to call him or her. So______ your teacher’s surname is Shu, you should call her "Shu laoshi". Being on time Being on time is ______ for Chinese students. Being at your desk before the bell rings is ______ you need to do in a Chinese classroom. Listening, not talking In China, teachers talk and students listen. Students ______ to ask questions, but most Chinese students are too ______ to open their mouth in class. So sometimes the teacher needs to ask somebody to answer questions. When studying Chinese in China, you will soon learn that it’s ______ hard work. You need to write the Chinese characters (汉字) and ______ your reading, speaking and listening. If you try your best, you will make it!
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