Which of the following are considered the basic components of an aircraft hydraulic system?

The basic components of an aircraft hydraulic system are best represented by the elements found in the first choice: reservoir, pump, tubing, selector valves, and actuating units. Each of these components plays a critical role in the hydraulic system's functionality.

The reservoir is essential for storing hydraulic fluid, ensuring that there is always a supply available for the pump. The pump is responsible for generating the hydraulic pressure needed to move the fluid throughout the system. Tubing, or lines, are the conduits that transport the hydraulic fluid between components. Selector valves are used to control the direction of flow and allow for the selective operation of different systems or components within the aircraft. Finally, actuating units convert the hydraulic pressure into mechanical motion, which is fundamental for operating various aircraft functions (such as landing gear and control surfaces).

Together, these components enable the hydraulic system to perform its essential functions, making this answer the most accurate representation of an aircraft hydraulic system's basic components.