medium and small colliery

• 中小煤矿

medium and small colliery的用法和样例：

例句

1. Medium and small coal mines in north of Shaanxi Province generally adopt longwall remaining coal pillars support mining.
   摘要长壁留煤柱支撑法开采是陕北中小煤矿普遍采用的一种采煤方法。
2. Many small and medium-sized coal mine production safety is still not solve the problem, this issue must not be the existence of trusting to luck, said Zhou Dadi.
   许多中小煤矿仍然不能解决安全生产问题，在此问题上绝不能存在侥幸心理，周大地说。