Which part of the aircraft controls the hydraulic system?

The hydraulic system of an aircraft is comprised of several components that work together to ensure efficient operation and control. Each of the parts mentioned serves a distinct function that is crucial for the hydraulic system's overall performance.

Reservoirs are essential as they store the hydraulic fluid, allowing for a consistent supply. The pumps then take this fluid from the reservoirs and generate the hydraulic pressure necessary for system operations. Valves play a critical role by controlling the flow and direction of the hydraulic fluid to various systems, such as landing gear, flight controls, and brakes.

Since the proper functioning of the hydraulic system relies on the integration of reservoirs, pumps, and valves to operate effectively, the comprehensive nature of this answer, encompassing all components, correctly identifies the complete framework responsible for the hydraulic system's operation. Therefore, it is clear that all these elements work together to ensure the hydraulic system functions properly, making the correct answer inclusive of all parts.