单项选择题 Battens are fitted in cargo holds across the frames of the vessel from the turn of the bilge upward. The purpose of these cargo battens is（）.

单项选择题 Ballast water can only be（）in cargo tanks in exceptional cases where the particular character of the operation of an oil tanker renders it necessary to carry ballast water in excess of the quantity required，provided that such operation of the oil tanker falls under the category of exceptional cases as established by the Organization.

单项选择题 Aboard ship，vertical flat plates running transversely and connecting the vertical keel to the margin plates are called（）.