graded coal

例句：

1. 1. The mine produces a variety of grades of coal for different industries.
   该矿生产多种不同等级的煤，供不同行业使用。
2. 2. The quality of the coal is determined by its grade.
   煤炭的质量由其等级决定。
3. 3. Coal mining requires careful sorting to ensure the highest grades are used for power generation.
   煤炭开采需要仔细分类，以确保最高等级的煤炭用于发电。