在杆上进行低压带电作业时，一般一根杆只允许（）工作。
A、三人
B、一人
C、二人
D、四人
参考答案：B
They have no idea at all___.
A．where he has gone
B．where did he go
C．which place he has gone
D．where has he gone
简述波能流？
