解释煤的氧化现象。
参考答案：
煤从矿井下开采以后，受空气中氧的作用，表面失去光泽，生出赤色或白色水锈，水分增高，块煤碎成粉末，这种现象称为氧化。
连词成句。
1. I, Ann, needs, think, help, some
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2. please, the station, is, where, me, excuse
3. the clothing shop, the post office, next to, is
4. about, a hundred meters, on the right, along, is, the hospital
5. places, different, Mr. Green, for, is looking
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