What point charges, all having the same magnitude, would you place at the corners of a square (one charge per corner), so that both the electric field and the electric potential (assuming a zero reference value at infinity) are zero at the center of the square?
A. negative on top, positive on bottom
B. positive on top, negative on bottom
C. positive on the left side, negative on the right
D. positive on one diagonal, negative on the other
E. negative on the left side, positive on the right