Which of the following is classified as a high-lift device?

High-lift devices are components that enhance the lifting capability of an aircraft's wings, particularly during low-speed operations such as takeoff and landing. Leading edge slats are examples of high-lift devices because they extend the wing’s surface area and alter its shape, allowing the wing to generate lift at lower speeds. This modification increases the critical angle of attack, preventing stall and enabling the aircraft to maintain controlled flight when it’s operating at slower velocities.

In contrast, ailerons, tailplanes, and rudders serve different purposes. Ailerons are primarily used for lateral control of the aircraft, allowing it to roll. The tailplane contributes to pitch control and stability, serving as a horizontal stabilizer. The rudder functions to control yaw, helping the aircraft turn and maintain directional stability. None of these components enhance lift directly in the way that leading edge slats do, which is why leading edge slats are identified as high-lift devices.