单项选择题
The time required for a lighted aid to complete a full cycle of light changes is listed in the Light List as the（）.
A.Set B.Frequency C.Period D.Function
单项选择题 The recording fathometer produces a graphic record of the（）.
单项选择题 The points on the earth’s surface where the magnetic dip is 90° are（）.
单项选择题 The four standard light colors used for lighted aids to navigation are red，green，white，and （）.
