A horse accelerates +2 mi/h/s south. Which option defines the horse’s acceleration?

The horse’s velocity increases by 2 mi/h every 1 s as the horse moves south.

The horse’s position decreases by 2 mi every 1 s as the horse moves south.

The horse’s speed changes to 2 mi/h as the horse moves south.

The horse’s speed decreases by 2 mi/h every 1 s.