Which of the flowing ____________ is true regarding Stokes-Einstein equation? (a) It is a theoretical method to estimate gas diffusivity at low pressure; (b) It is a theoretical method to estimate the diffusivity of a dilute solute in a liquid solvent where the size of solute molecule is much larger than that of solvent; (c) It is a theoretical method to estimate the diffusivity of a dilute solute in a liquid solvent where the size of solute molecule is much smaller than that of solvent; (d) It is a theoretical method to estimate the diffusivity of a concentrated solute in a liquid solvent where the size of solute molecule is much larger than that of solvent.