Which of the following describes one essential characteristic of a servo?

A key characteristic of a servo is that it requires feedback for precise control. Servos are designed to accurately control angular position, velocity, and acceleration. Unlike other motors that may operate solely based on a set input or command, servos use feedback mechanisms (such as encoders or potentiometers) to determine their actual position and adjust accordingly. This feedback loop is crucial in ensuring that the motor responds accurately and maintains the desired output.

In practical applications, this precise control allows servos to deal with varying loads and dynamic conditions effectively. By continually comparing the desired position to the actual position, the servo can make real-time adjustments, ensuring high performance in tasks that require accuracy, such as robotics, CNC machinery, and automated systems.

The other options do not reflect this key feature of servos. While continuous power supply and environmental adaptability can apply to various types of motors, they are not defining traits of servos specifically. Furthermore, the ability to work without reference input contradicts the fundamental principle of a servo, which is to rely heavily on feedback to achieve its operational goals.