单项选择题
A.horizontal motion of a white flag
B.letter K in Morse code given by light
C.code flag S as a hoist
D.firing of a white star signal
单项选择题 The service life of distress signals must be not more than（）.
单项选择题 The regulations require that inspected vessels on an international voyage，other than small passenger vessels，must carry which of the following distress signals on or near the navigating bridge?（）
单项选择题 The Navigation Rules state that a vessel shall be operated at a safe speed at all times so that she can be stopped within（）.