Suppose the Two Plates of a Parallel-Plate Capacitor Have Fixed $Q$

Suppose the two plates of a parallel-plate capacitor have fixed charges $Q$ and $-Q$ . If we double the gap between the plates, the:
-(b) the capacitor's capacitance,

A) quadruples.
B) doubles.
C) remains the same.
D) is reduced by a factor of two.
E) is reduced by a factor of four.
F) some other result (specify) .