井字架的第一导向滑轮与卷扬机距离应为多少？
参考答案：
卷扬机卷筒系带槽卷筒的为卷筒宽度的15倍，卷扬机卷筒系无槽卷筒的为卷筒宽度的20倍。
Mr. Robert is ________ our teacher. He is also our friend.
A．no more than
B．less than
C．more than
D．no less than
简述干法净化定义。
