Final answer:
The best reference point to show the ball was in motion is 'c. The house in the background', as it remains stationary and provides a clear backdrop to observe the ball's changing position over time.
Step-by-step explanation:
The best example of a reference point that could be used to show a ball was in motion while Mia was playing catch with her younger brother in the yard is c. The house in the background. A reference point should be stationary relative to the observer and should provide a clear indication that the object (the ball in this case) is changing position over time. The house provides a static background against which the motion of the ball is easily seen and measured.
The position of the Sun in the sky is not ideal as it changes position throughout the day due to Earth's rotation. A tree's height does not provide a lateral reference point to indicate motion. A ball's speedometer, if it had one, would provide numerical data on speed, but it's not a visual reference point for observing motion.
To understand motion, it is essential to have a clear, fixed reference point to determine changes in an object's position. In various scenarios, the choice of reference point can show either motion or rest, depending on the observer's point of view.