接触短路引弧法可以用较低的空载电压产生焊接电流。( )
参考答案：对
_____ of the students who took part in the military training is 450.
A．A number
B．A lot
C．A few
D．The number
无线电话的紧急信号是（）
A.PANPAN
B.PANPAN三次
C.XXX
D.XXX三次
