单项选择题
A.three shapes，the highest and lowest shall be red balls，and the middle shall be a white diamond
B.two black balls
C.three shapes; the highest and lowest shall be black balls，and the middle shall be a red diamond
D.three shapes; the highest and lowest shall be black balls and the middle shall be a black diamond
单项选择题 During the day，a dredge will indicate the side on which it is safe to pass by displaying（）.
单项选择题 During the course of a voyage，a seaman falls on the main deck and injures his ankle. The Master should submit a Report of Marine Accident，Injury or Death if the（）.
单项选择题 During storm conditions on a ship，the mooring tensions should be adjusted so that（）.