单项选择题
（）is the navigational timekeeper of the vessel.
A.The marine sextant B.The chronometer C.The magnetic compass D.The gyrocompass
单项选择题 （）is used for measuring horizontal and vertical angles.
单项选择题 （）means rudder to be held in the force and aft angles.
单项选择题 （）means check the swing of the vessel’s head in a turn.
