The following statements concern how to increase the rate of diffusion (in kg/s). All but one statement are always true. Which one is not necessarily true? 

(a) Increase the cross-sectional area of the diffusion channel, keeping constant its length and the difference in solute concentrations between its ends. 

(b) Increase the difference in solute concentrations between the ends of the diffusion channel, keeping constant its cross-sectional area and its length. 

(c) Decrease the length of the diffusion channel, keeping constant its cross-sectional area and the difference in solute concentrations between its ends.

(d) Increase the cross-sectional area of the diffusion channel, and decrease its length, keeping constant the difference in solute concentrations between its ends. 

(e) Increase the cross-sectional area of the diffusion channel, increase the difference in solute concentrations between its ends, and increase its length.