單項選擇題明挖爆破時,起爆信號是()。

A.鳴30s、停、鳴30s、停、鳴30s
B.鳴20s、鳴10s、停、鳴20s、鳴10s、停、鳴20s、鳴10s
C.鳴10s、停、鳴10s、停、鳴10s
D.鳴20s、停、鳴20s、停、鳴20s