Consider a capacitor of capacitance $C$, with plate area $A$ and plate separation $d$, filled with air [Fig. (a)]. The distance between the plates is increased to $2d$ and one of the plates is shifted as shown in Fig. (b). The capacitance of the new system now is : (A) $\frac{C}{4}$ (B) $\frac{C}{2}$ (C) $2C$ (D) $4C$