单项选择题
A.hold your course and speed
B.sound the danger signal
C.begin an exchange of passing signals
D.do not cross the channel if you might impede the other vessel
单项选择题 The disinfection of various compartments in a vessel by filling with a gaseous agent to destroy rats and all insects pests which act as germ carriers means（）.
单项选择题 Backing means the wind（）.
单项选择题 When a feature remains in its existing charted position but has a change of characteristic,（）command is used on a chart.