When you select a cockpit control to lower the flaps, which element of the primary hydraulic system is responsible for activating the corresponding actuator?

The correct choice is the electrical selector valve, which plays a crucial role in the operation of the hydraulic system for lowering the flaps. When a cockpit control is selected to lower the flaps, the electrical selector valve responds to the input from that control.

This valve directs hydraulic fluid to the appropriate actuator, allowing it to move and adjust the flaps as needed. The electrical selector valve acts as a bridge between the cockpit inputs and the hydraulic actuators, ensuring that the correct action is taken based on the pilot's inputs.

Understanding the purpose of the other elements helps clarify why they do not fulfill this specific function. The hydraulic accumulator serves to store hydraulic fluid under pressure for use when needed but does not activate actuators directly. The pressure regulator is responsible for maintaining the correct pressure within the hydraulic system but does not control the actuator movements. The pneumatic actuator, however, uses air pressure rather than hydraulic fluid to move components and is not involved in the flap operation, which relies directly on the hydraulic system.