The graph shows the motion of a horse during the first portion of a race. a The horse maintained a constant acceleration during this portion of the race. b The horse maintained a constant velocity during this portion of the race. c The horse increased its acceleration during this portion of the race. d The horse decreased its velocity during this portion of the race.

Based on the information given, it is not possible to determine with certainty which option is correct. The graph only shows the position of the horse over time and does not provide information about its velocity or acceleration directly. To determine which option is correct, we would need additional information such as the time intervals and corresponding velocities or accelerations.