Which area of the aircraft is designated for the lavatory?

The cabin is the correct answer because it is the main area of the aircraft where passengers are seated and includes spaces designated for various passenger amenities. Within the cabin, there are dedicated lavatory sections that provide restrooms for passengers, ensuring convenience and privacy during the flight. This area is specifically designed to accommodate lavatories, which are essential for passenger comfort.

The cockpit refers to the area where the pilots control the aircraft and does not include any passenger facilities such as lavatories. The galley is the area where food and beverages are prepared and stored for service but also does not contain lavatories. The service area is focused on the operational aspects of serving passengers and might include areas for flight attendants to manage supplies or equipment, but it primarily does not serve as a location for lavatories either. Thus, the cabin is distinctly the area that includes the lavatory facilities for passenger use.