Final answer:
The correct word to complete the sentence is 'dismount,' as it specifically means to get off a horse, which is the action described after Shaye's morning ride.
Step-by-step explanation:
The word that best completes the sentence 'Shaye rode her horse up to the stable and _____ after a satisfying morning ride.' is C. dismount. To dismount means to get off a horse, bicycle, or motorcycle. The other options do not fit contextually with riding a horse and coming to the stable after a ride. To unhitch would mean to detach something that is hitched like a trailer, not a rider from a horse. Dissatisfy is not appropriate as it means to fail to satisfy someone, which is not relevant to the action of getting off a horse. Finally, to unsaddle would mean to remove the saddle from the horse, which might happen after dismounting, not as a synonym for getting off the horse.