grade of coal

例句：

1. 1. The grade of coal isdetermined by its moisture content and ashcontent.
   煤的等级由其水分和灰分含量决定。
2. 2. Coal mining companiesneed to ensure that the grade of coalmeets their standards.
   煤矿公司需要确保煤炭的等级符合他们的标准。
3. 3. Thegrade of coal has asignificant impact on the energy efficiencyof the power generation system.
   煤炭的等级对发电系统的能源效率有重大影响。