A、After determining that the frequency or channel appears to be no longer in use
B、After determining that geographic distance from the distress situation will prohibit any other signal from interfering with emergency communications
C、After the Rescue Coordination Center transmits a message on the frequency or channel being used for emergency communications stating that such traffic has concluded
D、Routine communications can resume if，in the Master's opinion，communications on that frequency or channel will not interfere with emergency communicatio