牵引网的电压损失，等于牵引变电所牵引侧（）电压与电力机车受电弓上电压的算术差。
参考答案：母线
—Listen! There is a knock on the door. Who _____ it be?
—It must be Jack. Just now I sent for him. [ ]
A. shall
B. can
C. must
D. might
简述WindowsNT的结构.
