为什么刮板输送机必须使用拨链器？
参考答案：
拨链器使绕过链轮的链子迅速脱离链轮，避免链轮继续拖卷堆积并卡住链子，造成断链或打齿等事故。
句型转换。
1. You will be at home this evening. (变为否定句)
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2. She is going to the park this afternoon. (变为一般疑问句)
3. You must clean the bedroom before you go out. (对画线部分提问)
4. Their little daughter is going to be five next year. (对画线部分提问)
摄氏温度是把___________的温度规定为零度，-25℃应该读作_______________。
