单项选择题
The extension of the after part of the keel in a single-screw vessel upon which the stern post rests is called the（）.
A.boss B.knuckle C.skeg D.strut
单项选择题 For existing ships，（）is not an improvement to safety.
单项选择题 Floors aboard ship are（）.
单项选择题 （）is not a static load.
