单项选择题
A.orbiting satellites in space
B.commercial radio stations
C.private，commercial，and military aircraft
D.ordinary radio stations
单项选择题 All self-propelled vessels on an international voyage must be equipped with how many Emergency Position Indicating Radiobeacons (EPIRB)（）?
单项选择题 A vessel operating outside of coastal waters must carry an automatically activated Emergency Position Indicating Radio Beacon (EPIRB) if she（）.
单项选择题 A major advantage of the NAVTEX system when compared to other systems is that（）.