单项选择题
However, reception of certain types of MSI messages, such as shore to ship distress alerts and navigational and meteorological warning are（）.
A.selective and can be suppressed by ships B.mandatory and can not be suppressed by ships in the affected area C.not very important so that ships don‟t require them D.received by all ships wherever they are
单项选择题 The International SafetyNet Service is able to address the call to（）.
单项选择题 DSC distress relays can be transmitted by either（）or（）.
单项选择题 On-scene communications will normally take place between（）.
