单项选择题
A.sagging with tensile stress on main deck
B.sagging with compressive stress on main deck
C.hogging with tensile stress on main deck
D.hogging with compressive stress on main deck
单项选择题 Why is it necessary to extend ventilators of gasoline powered vessels to the bilges（）.
单项选择题 While cranking out a quadrantal davit，slippage of the quadrant due to excessive wear or failure of the teeth in the quadrant will cause the（）.
单项选择题 Which term refers to a transverse curvature of the deck（）.