9. Which of the following best explains why a hot air balloon rises and floats in air?
A. Air particles inside the balloon are farther apart, causing its density to be higher than the density of air outside the balloon.
B. Air particles inside the balloon are farther apart causing its density to be less than the density of air outside the balloon.
C. Air particles inside the balloon are closer together, causing its density to be higher than the density of the air outside the balloon.
D. Air particles inside the balloon are closer together, causing its density to be lower than the density of the air outside the balloon.