明挖爆破时 起爆信号是( )。A.鸣30s 停 鸣30s 停 鸣30sB.鸣 20s 鸣10s 停 鸣20s 鸣10s

明挖爆破时，起爆信号是（）。

A.鸣30s、停、鸣30s、停、鸣30s

B.鸣 20s、鸣10s、停、鸣20s、鸣10s、停、鸣20s、鸣10s

C.鸣10s、停、鸣10s、停、鸣10s

D.鸣20s、停、鸣20s、停、鸣20s

请帮忙给出正确答案和分析，谢谢！