A positively charged plastic rod of charge +Q is held at the same distance d from three small spheres of identical mass and radius:
1. Sphere A: neutral aluminum (conductor)
2. Sphere B: neutral wood (insulator)
3. Sphere C: wood carrying a net charge +Q
Rank the magnitudes of the electrostatic forces exerted on the spheres from greatest to least.
a) A > C > B
b) C > A > B
c) A > B > C
d) C > B > A