单项选择题
The（）provides the link between the Space Segment and the land-based National/International fixed communications networks.
A.VHF B.SART C.NAVTEX D.LES
单项选择题 Reliable delivery of messages is ensured by（）techniques.
单项选择题 How long must the GMDSS radio log be retained on board（）.
单项选择题 Each satellite broadcasts（）traffic on a designated channel.
