单项选择题
A.observer's meridian
B.Greenwich meridian
C.body's meridian
D.zenith distance
单项选择题 An authorized light to assist in the identification of submarines operating on the surface is a(n)（）.
单项选择题 An aneroid barometer on a boat should always be（）.
单项选择题 An anchored vessel is servicing an aid to navigation and is restricted in her ability to maneuver. Which lights will she show? （）