单项选择题
The GMDSS must combine all various subsystems, because（）.
A.they all have different limitations with respect to coverage B.they all have different limitations in the technology they use C.different systems apply to different ships D.all of above
单项选择题 （）communication are intership VHF radio telephone communication.
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 geostationary orbit.
