Which of the following describes a key function of the rudder on a UA?

The rudder on a Unmanned Aircraft (UA) plays a crucial role in managing directional movement, which is a fundamental aspect of aircraft control. The rudder is primarily used to control the yaw of the aircraft, allowing it to turn left or right. By adjusting the angle of the rudder, pilots (or, in the case of UAs, the control system) can influence the movement of the aircraft around its vertical axis, making it essential for navigating and maintaining flight paths.

Other options, such as controlling speed, altering altitude, or monitoring fuel levels, do not pertain to the rudder's function. Speed is typically managed by the throttle or engine control systems, altitude is adjusted through the use of elevators or other aerodynamic surfaces, and fuel levels are monitored by instruments that assess the amount of fuel remaining in the tanks, independent from the rudder's operations. Therefore, the primary purpose of the rudder is indeed to manage directional movement, which is why this answer is the most accurate in the context of the question.