单项选择题
A.Once a day
B.At the change of every watch
C.Only when in fresh or brackish water
D.Prior to getting underway
单项选择题 When is the density of the water required to be logged in the logbook of a ship?（）
单项选择题 When are fore and aft draft readings required to be entered in the unofficial logbook of a ship? （）
单项选择题 When an azimuth of the Sun has been taken and the deviation of the standard magnetic compass computed，the watch officer should record the results（）.