单项选择题
A Navtex station in each NAVAREA is usually allowed to have（）for transmission.
A.10 minutes every 4 hours B.half an hour every other hour C.irregular period of time D.5 minutes every two hours
单项选择题 It is possible for ships to receive safety message transmitted by Navtex station（）.
单项选择题 The frequency 518KHZ will be used to transmit（）and（）wanings in NAVTEX.
单项选择题 Distress alerts will be relayed on the（）when the RCC considers it necessary.
