单项选择题
General communications are those communications（）.
A.between ship stations and shore-based communication networks B.concern the management and operation of ships C.may have an impact of the safety on ships D.all of A, B, C
单项选择题 What’s the advantage when using the satellites?（）
单项选择题 Some radio waves（）the surface of the earth because of its（）.
单项选择题 Ships equipped with Inmarsat SES send distress alerts both（）.
