单项选择题
A.remains aligned with compass north B.also turns to starboard C.first turns to starboard then counterclockwise to port D.turns counterclockwise to port
A.spider element B.mercury ballistic C.gyrotron D.rotor
A.the horizontal component of the permanent magnetism B.deviation caused by the vessel's inclination from the vertical C.induced magnetism in the horizontal soft iron D.induced magnetism in the vertical soft iron