Two Metal Spheres on Insulating Stands Have the Same Positive $Q$

Two metal spheres on insulating stands have the same positive charge $Q$ . If we reduce the distance between the spheres' centers by a factor of two, the magnitude of the repulsive force between the spheres increases by

A) a bit less than a factor of two.
B) exactly a factor of two.
C) a bit more than a factor of two.
D) a bit less than a factor of four.
E) exactly a factor of four.
F) a bit more than a factor of four.