Which of these would be a good model to demonstrate the fact that the galaxies are moving apart as the universe is expanding? a) the spots on the balloon move away as the balloon is inflated b) dust particles move around in random directions c) pieces of paper scatter in random directions in the wind d) cars travel down a highway in forward motion.

Option A: The spots on the balloon move away as the balloon is inflated.

one of the scientific models describes the galaxies are moving apart as the universe is expanding. This expansion theory came from the observation of red-shifted spectrum from all the directions indicating that the galaxies are moving away.  This can be understood from the inflated balloon. Initially spots can be marked using a colored pen on the balloon.On inflating the balloon, it would be noticed that the spots on the balloon move away. Actually the position of the spots won't change, but the distance between the spots would expand. This is a good model to explain the expanding universe. The galaxies are neither moving in any random direction nor moving forward. So, rest of the options are not good models to explain the theory.