In the SDS-PAGE (Sodium Dodecylsulfate - Polyacrylamide Gel Electrophoresis) Method

In the SDS-PAGE (sodium dodecylsulfate - polyacrylamide gel electrophoresis) method, separation takes place on the basis of

A) charge only, because all particles have different charges, but the same mass.
B) the sieving action of the gel, because all particles have the same charge, but different masses.
C) the sieving action of the gel, because all particles have approximately the same charge\mass ratio, but different masses.
D) the chemical nature of the buffer used as the electrolyte.