施工中如果发现没有井口信号,应首先测试()。
A.电源电压
B.电台发射距离
C.炮线及检波器电阻
D.通讯电路
参考答案:C
The train hasn't arrived yet. Could you tell me ______? [ ]
A. why the train is late
B. that the train can come on time
C. when will the train arrive
D. why does the train arrive late
刀具的几何角度中,常用的角度有()、()、()、()、()和()六个。