单项选择题
Mariners can use DSC for（）.
A.general communication B.distress alerting and safety calling C.receive MSI D.both B and C
单项选择题 Equipment requirement vary according to（）.
单项选择题 The WWNWS establishes three types of navigational warning:（）.
单项选择题 Every ship must fitted with（）SART, and（）two-way VHF radio telephone.
