One student made a science model with a balloon having many spots on it. the balloon was blown up gradually as shown below. a girl blowing up a balloon with dots on it. the dots are close together and concentrated in one area before the balloon is blown up. as the balloon expands the dots are spread further apart. what is best demonstrated by this model? a. galaxies move closer when the universe expands b. density of particles in space decreases when the universe expands c. gravitational force determines the distribution of matter in the universe d. gravitational force on galaxies decreases when the universe expands