单项选择题
Within the polar areas it is（）to see a satellite in geostationary orbit.
A.impossible B.possible C.easy D.difficult
单项选择题 The position of INMARSAT AOR-W satellite is（）above the equator.
单项选择题 The complying vessels can transmit ship-to-shore distress alerts by at least（）.
单项选择题 The GMDSS is a world-wide communication network combining（）with（）.
