单项选择题
A.filling a partially filled tank
B.using an on board crane to lift a freely swinging heavy object
C.emptying a partially filled tank
D.transferring ballast from the forepeak to the after peak
单项选择题 A vessel is equipped with twin propellers，both turning outboard with the engines half ahead. If there is no wind or current and the rudders are amidships，what will happen?（）.
单项选择题 A twin-screw vessel with a single rudder is making headway. The engines are full speed ahead. There is no wind or current. Which statement is FALSE?（）.
单项选择题 A single-screw vessel going ahead tends to turn more rapidly to port because of propeller（）.