单项选择题
The Inmarsat system is open for use by（）countries on a non-discriminatory basis.
A.some B.lots of C.many D.all
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（）.
单项选择题 The complying vessels can transmit ship-to-shore distress alerts by at least（）.
