The II3123 face is a light type caving face of three-soft coal seam.the roof is cracked,sloughing and roof fall often occur.是什么意思_The II3123 face is a light type caving face of three-soft coal seam.the roof is cracked,sloughing and roof fall often occur.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句