A man aboard a vessel，signaling by raising and lowering his outstretched arms to each side，is indicating（）.

A.danger，stay away

B.all is clear，it is safe to pass

C.the vessel is anchored

D.a distress signal

SF₆电压互感器吸附剂更换时对户内设备，应先开启强排通风装置30min后，方可进入，工作过程中应当保持通风装置运转。