单项选择题
A.one meter from the tank bottom and one meter below the tank top
B.one half the ullage of the tank and one meter below the tank top
C.one half the ullage of the tank and one meter above the tank bottom
D.at three meter intervals from the tank top
单项选择题 When a cargo boom or crane is rated at varying capacities，there will be a table at the controls which relates safe working load to（）.
单项选择题 When（）clean ballast water from any vessel，an application shall be made to Harbor Authorities for approval.
单项选择题 When checking the oxygen content of the cargo tanks prior to loading cargoes requiring vapor recovery，the atmosphere must be sampled（）.