单项选择题
Within the polar areas it is（）to see a satellite in geo-stationary orbit .
A.impossible B.possible C.easy D.difficult
单项选择题 The quality of the message can be affected by（）.
单项选择题 The complying vessels can transmit ship-to-shore distress alerts by at least（）.
单项选择题 GMDSS is to provide（）with reliable communication .
