What distinguishes a "sock" marking from a "stocking" marking?

The distinction between a "sock" marking and a "stocking" marking is fundamentally tied to their characteristic lengths and coverage on a horse’s leg. A "sock" marking is indeed a shorter leg marking, generally confined to the area below the fetlock, while a "stocking" marking extends higher up the leg, covering more area and often reaching up to the knee. Thus, a "sock" marking is always shorter than a "stocking" marking, which makes the choice provided correct.

Understanding these definitions is crucial for identifying horse markings accurately, especially when assessing and distinguishing breeds or individual horses in practice. The other choices do not capture the essence of the difference in height and coverage between the two types of markings.