Identify a primary flight control of an aircraft.

Ailerons are indeed classified as primary flight controls of an aircraft. They are located on the trailing edge of the wings and are used to control the aircraft's roll about its longitudinal axis. When a pilot moves the control yoke or stick, one aileron deflects upward while the other deflects downward, creating a difference in lift between the wings. This difference causes the aircraft to roll towards the wing with the upward-deflected aileron.

In contrast, flaps and spoilers serve secondary functions. Flaps are used to increase lift during takeoff and landing, allowing for slower flight speeds. Spoilers are primarily used to reduce lift and increase drag, particularly during descent and landing phases to help slow the aircraft down. Trim devices adjust the position of flight controls to relieve pilot workload but do not directly control the aircraft's attitude in the same way that ailerons do.

Thus, among the options provided, ailerons are designated as primary flight controls and play a critical role in the maneuverability and stability of an aircraft during flight.