category of direct roof

• 直接顶分类

category of direct roof的用法和样例：

例句

1. According to the studying and acquainting with the direct roof control of Datong mining area,this paper offers a kind of simple and workable classification for direct roofs.
   根据作者对大同矿区直接顶板控制的研究和了解，提出了一种简单易行的直接顶分类方法。