Three separate two-charge systems are arranged as follows.
• System A: +q and +q separated by distance d
• System B: +q and −q separated by distance 2d
• System C: −q and −q separated by distance d
Which ranking correctly orders the electric potential energies U_A, U_B, and U_C from most positive to most negative?
a) UA>UB>UC
b) UB>UA=UC
c) UA=UC>UB
d) UA>UC>UB