掘进工作面的通风采用“三专”供电是指哪“三专？
参考答案：
专用变压器、专用线路、专用开关。
Having taken our seats, ______.
A．the professor began the lecture
B．the lecture began in no time
C．we were attracted by the lecture immediately
D．the bell announced the beginning of the lecture
采购是企业物流管理的起始点，按需采购是前提原则，要尽量做到费用最小。（）
