单项选择题
In twin-screw engine installations while going ahead，maneuvering qualities are most effective when the tops of the propeller blades both turn（）.
A.to starboard B.outboard from the center C.to port D.inboard toward the center
单项选择题 In towing，heaving lines are used for（）.
单项选择题 In towing it is desirable for the tug and the vessel to ride wave crests simultaneously because（）.
单项选择题 In order to back a right-handed，single-screw vessel in a straight line，you will probably need to use（）.
