Which of the following is not a location for the lavatory manual water shut-off valves?

The correct answer is that the center lavatory is not a location for the lavatory manual water shut-off valves. In aircraft design, the layout of lavatory systems typically comprises forward and aft lavatories, which accommodate the water and waste management needs. Each of these areas is equipped with manual shut-off valves to maintain the functionality of the lavatories while allowing for service and maintenance as necessary.

The term "center lavatory" may not refer to a specific operational area in many aircraft as there is typically no designated central lavatory with such shut-off features. Instead, designs generally focus on providing lavatory services in the forward and aft compartments, which helps with space utilization and passenger access.

Regarding the other options, the forward lavatory and aft lavatory both have designated valves to manage water flow. Additionally, water shut-off valves can often be found under the sinks, as this location allows easy access for crew members and maintenance personnel when servicing the lavatory systems. These practical considerations guide the design and placement of such components in aviation.