单项选择题
If several fixed navigational lights are visible at the same time，each one may be positively identified by checking all of the following EXCEPT what against the Light List?（）
A.Rhythm B.Period C.Intensity D.Color
单项选择题 How is variation indicated on a small-scale nautical chart?（）
单项选择题 Gyrocompass repeaters reproduce the indications of the master gyrocompass. They are（）.
单项选择题 Error may be introduced into a magnetic compass by（）.
