The drains of lavatory sinks are fitted with P-type or S-type traps to __________.

Correct Answer: Option D — provide a seal against sewer gas rising into the compartment

P-type and S-type traps are essential plumbing components that maintain a permanent water seal. This seal acts as a physical barrier, preventing hazardous sewer gases and odors from entering the ship's living or working spaces through the drain lines, as required by standard marine sanitation and health safety regulations.