露天矿台阶的构成要素有上部平盘、下部平盘、台阶高度、台阶坡面、台阶坡面角、台阶顶底线、（）。
参考答案：台阶坡底线
The development of China's economy ________ since the 80s of last century. [ ]
A. has been accelerating
B. had accelerated
C.is accelerating
D. accelerated
逻辑文件的定义及引入逻辑文件的好处。
