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美国的煤炭工业已进行了重大调整（90年代政策正在调整）。虽然煤炭产量逐年稳步增加，但煤价一直很低‘选煤厂的数量也持续减少。有一些趋势可从80年代初以来生产中的选煤厂数中一些趋势分析出。根据出版的基斯顿煤炭工业手册上提供的关于选煤厂的统计数字，可以回顾1976年、1
The coal industry in the United States has undergone major adjustments (policies are being adjusted in the 1990s). Coal production has been steadily increasing year by year but coal prices have been very low. The number of coal preparation plants has also continued to decrease. There are some trends that can be analyzed from the trends in the number of coal preparation plants in production since the early 1980s. According to the published statistics on the coal preparation plant provided by the Gisborne Coal Industry Manual, it can be recalled that in 1976 1