When a vessel signals her distress by means of a gun or other explosive signal，the firing should be at intervals of approximately（）.

A.To ensure that interference to proprietary communications is minimized
B.To ensure that only voice communications can be effected on the distress frequency or channel
C.To ensure that a distressed vessel will have a "window" twice each hour for transmitting routine messages
D.To ensure that interference on a particular frequency or channel to communications concerning emergency traffic is minimized

A.1492 kHz
B.1892 kHz
C.2082 kHz
D.2182 kHz

A.Red flares or red rockets
B.Continuous sounding of fog signaling apparatus
C.International Code Flags "November" and "Charlie"
D.Basket hanging in the rigging