单项选择题
A.Cold fronts are more violent and of shorter duration
B.Cold fronts are milder and last longer
C.They are very similar with the exception of wind direction
D.Warm fronts are more violent and of longer duration
单项选择题 The principal purpose of adjustment of the magnetic compass is to eliminate（）as far as possible.
单项选择题 You are standing the wheelwatch on entering port and the master gives you a rudder command which conflicts with a rudder command from the pilot.What should you do?（）
单项选择题 （）is used for lifting cargo.