The time required for molecules in a solution to move from A to B is proportional to the square of the distance from A to B. What property of diffusion does this principle explain?

a) Diffusion is rapid over short distances but slow over longer distances.
b) Diffusion rate is directly proportional to distance.
c) Diffusion is inversely related to molecular weight and size.
d) The rate of diffusion depends upon the concentration gradient of the molecule.