明挖爆破时准备信号是( )。
2023-05-10
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
参考答案:B
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
参考答案:B
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