单项选择题
International distress signal in VHF calling for help is（）.
A.Help，Help，Help B.Mayday，Mayday，Mayday C.Save，Save，Save D.Rescue，Rescue，Rescue
单项选择题 There are salvage operations（）position 120.0N 12.5E.
单项选择题 When it is accepted to remain on the frequency indicated，you should say（）.
单项选择题 When the changing of a VHF channel / frequency is accepted，say（）.
