单项选择题
The difference between international and national Navtex Service is limited to（）.
A.frequency allocated B.both language and frequency C.language used D.transmission power and time
单项选择题 A Navtex station in each NAVAREA is usually allowed to have（）for transmission.
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.
