单项选择题 If no distress acknowledgement is received（）a DSC distress call transmission, then the ship in distress may repeat the DSC distress call attempt after a delay of between 3.5 and 4.5 minutes from the beginning of the initial call.

单项选择题 What’s the abbreviation for the World Meteorological Organization?（）

单项选择题 Geostationary satellites are the artificial satellites which（）.