Which signal is recognized as a distress signal?

A、Whichsignalisrecognizedasadistresssignal?
B、Whichsignalisrecognizedasadistresssignal?
C、Whichsignalisrecognizedasadistresssignal?
D、Whichsignalisrecognizedasadistresssignal?
E、Whichsignalisrecognizedasadistresssignal?
F、Whichsignalisrecognizedasadistresssignal?G:Whichsignalisrecognizedasadistresssignal?H:Whichsignalisrecognizedasadistresssignal?