单项选择题
Which message categories cannot be disabled by the GMDSS radio operator（）.
A.Navigational Warnings B.Meteorological Warnings C.Search and Rescue Information D.All of the above
单项选择题 Which maintenance functions can a GMDSS Radio Operator perform（）.
单项选择题 Which device provides the main means in the GMDSS for locating ships in distress or their survival craft（）.
单项选择题 Which action should be taken on receipt of a GMDSS distress alert（）.
