In Circuit Shown Two Identical Parallel Plate Capacitors Are Connected

In circuit shown two identical parallel plate capacitors are connected.Initially the space between the plates of each capacitor is filled with air.If we wish to double the total amount of charge stored on both capacitors for the same applied voltage,which material should we use to fill the space between the plates?

A) Fill C₁ with glass (dielectric constant of 4) and leave C₂ alone.
B) Fill C₁ with Teflon (dielectric constant of 2) and leave C₂ alone.
C) Fill both C₁ and C₂ with Teflon (dielectric constant of 2) .
D) Fill both C₁ and C₂ with glass (dielectric constant of 4) .