What is the primary purpose of the aircraft's control surfaces?

The primary purpose of the aircraft's control surfaces is to manipulate the aircraft's flight path. Control surfaces include ailerons, elevators, and rudders, which work in unison to control the aircraft's orientation and movement in three-dimensional space. These surfaces allow the pilot to perform essential maneuvers such as turning, climbing, descending, and stabilizing the aircraft during flight.

Ailerons are located on the wings and control roll, allowing the aircraft to tilt sideways. Elevators are found on the tail and control pitch, enabling the aircraft to ascend or descend. The rudder, also located on the tail, controls yaw, or the left and right movement of the aircraft's nose. By using these control surfaces, pilots can accurately direct the aircraft according to their flight objectives and respond to changing flight conditions.

The other options describe functions that are not directly related to the manipulation of flight path. Measuring airspeed, assisting with fuel management, and regulating cabin pressure are important systems in an aircraft, but they do not influence the control of the aircraft's movement in the air. Thus, the manipulation of the flight path through control surfaces is the fundamental function that defines their role in aviation.