“hard coal”可以造什么句,hard coal造句
来源:语文精选馆 2.35W
anthracite; hard coal
The first caving roof sections in hard coal layers can effectively reduce the pressure during the course of caving and guarantee safe production and efficiency.
Finally great depth of burial, long time and higher temperature may metamorphose the lignite into soft coal or bituminous coal and in extreme cases, to hard coal or anthracite.
hard coal; anthracite