单项选择题
DSC distress relays can be transmitted by either（）or（）.
A.a coast station/a ship station B.an EPIRB/a SART C.ARQ/FEC D.a back-up satellite/a land SAR unit
单项选择题 On-scene communications will normally take place between（）.
单项选择题 （）are used for distress alerting as a rule.
单项选择题 Mariners can use DSC for（）.
