单项选择题
With the help of GMDSS（）can be alerted to a distress incident as soon as possible.
A.all ships in a large sea area B.only the sea authorities ashore C.the SAR units ashore and at sea D.the port radios and the coast stations
单项选择题 The Inmarsat system is open for use by（）countries on a non-discriminatory basis.
单项选择题 Within the polar areas it is（）to see a satellite in geo-stationary orbit .
单项选择题 The quality of the message can be affected by（）.
