Which One of the Following Statements Concerning Diffusion Is True

Which one of the following statements concerning diffusion is true?

A) Diffusion occurs only in gases.
B) Diffusion occurs in solids and fluids.
C) Diffusion is described by Boyle's law.
D) The SI unit for the diffusion constant D is m/s².
E) Diffusion occurs when molecules move from regions of lower concentration to regions of higher concentration.