單項選擇題

why do some stations keep silence?（）

A.Because they are not engaged in the distress traffic
B.they will affect the transmission of the distress traffic
C.The powers of these stations are very weak
D.They are not in charge of search and rescue

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What channel is general communication used?（）

A.any appropriate channel except public communication
B.any appropriate channel except for public communications
C.any appropriate channel besides public communication
D.any appropriate channel beside public communication

單項選擇題

What’s the advantage when using the satellites?（）

A.The message can be directed to the desired location
B.The message can follow the earth’s curvature
C.The quality of message can not be affected by climatic
D.The range of the message extend and the quality of reception is improved