Which of the following is classified as an artificial riding aid?

An artificial riding aid is a tool that a rider uses to assist and enhance communication with their horse, often to influence the horse’s movement or behavior. The crop, or whip, is designed specifically for this purpose; it provides additional cues to the horse, signaling to them to move forward or respond in a certain way.

In contrast, the legs, seat, and voice are natural aids that riders use to communicate with their horses. The legs and seat refer to the rider's physical position and pressure used for guidance, while the voice involves vocal commands that can encourage or direct the horse. These natural aids rely on the rider's body and voice rather than a tool. Therefore, the crop stands out as the artificial riding aid among the options presented.