单项选择题
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
单项选择题 What channel is general communication used?（）
单项选择题 What’s the advantage when using the satellites?（）
单项选择题 Any ships fitted with SES can（）and（）through the satellite system when sending a distress alert.
