单项选择题
NAVTEX transmissions have a designed range of about（）nautical miles.
A.300 B.400 C.500 D.600
单项选择题 The NAVTEX receiver can be mounted on（）.
单项选择题 Ships at sea are in urgent need of MSI because they are（）various kinds of danger.
单项选择题 In the GMDSS, MSI broadcasts will be made on two dedicated systems:（）and（）.
