什么叫局部瓦斯积聚？
参考答案：
在采掘工作面及其他巷道内体积大于0.5立方米空间中积存的瓦斯浓度达到2%时，称为瓦斯积聚。
I often see Tom on the playground. When I passed the playground yesterday, I saw him .
A. play; playing B. to play; play C. playing; to play C. playing; play
当列车管减压时，分配阀主阀下移，滑阀下移，工作风缸的风压去容积室。
