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（）.

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.