Four charges are placed very closed to each other, as shown. The separation between the two charges on the y-axis is a. The separation between the two charges on the x -axis is also a. The leading order (non-vanishing) form of the electrostatic potential, at point P, at a distance from the origin (ra), is P (a) (c) 1qa (3-1) 2002 qa (5-1) a +9 +q 0 60 -9 -9 a (b) (d) 1 2qa 4E 1 qa (1-3)