The Capacitance of a Parallel Plate Capacitor Changes When a Dielectric

The capacitance of a parallel plate capacitor changes when a dielectric is inserted between the plates. This is mainly due to

A) the existence of denser matter than air or vacuum, which forms a barrier for electric field lines and reduces the electric field in the region.
B) the polarizability of the material, which sets up an electric field opposite to the applied field, thus reducing the electric field strength in the region.
C) the fact that dielectrics have excess charge that then "shields" the plates from each other, reducing the electric field in the region.
D) None of these.