根据《生产安全事故报告和调查处理条例》规定，特别重大事故是指造成（）人以上死亡事故。

A、20

B、50

C、40

D、30

Which condition represents the appropriate time for setting off distress flares and rockets? （）

A.Only when there is a chance of their being seen by rescue vessels

B.At half hour intervals

C.At one hour intervals

D.Immediately upon abandoning the vessel