The correct answer is A) All watertight doors in subdivision bulkheads shall be kept closed during navigation except when necessarily opened for working of the vessel, and in such cases they shall always be ready to be immediately closed. This is the correct answer because it aligns with standard operating procedures for maintaining watertight integrity on passenger vessels as per maritime regulations. Keeping watertight doors closed during navigation, except when necessary for operations, helps maintain the vessel's watertight subdivision and enhances safety in the event of damage or flooding. The other options are incorrect as they either leave the doors open during navigation, which compromises watertight integrity, or only close them when at anchor or during adverse weather, which does not provide the necessary level of safety for a vessel carrying over 1,200 passengers.