Four Charged Particles (Two Having a Charge +Q and Two

Four charged particles (two having a charge +Q and two having a charge -Q) are arranged in the xy-plane, as shown in the figure. These particles are all equidistant from the origin. The electric potential (relative to infinity) at point P on the z-axis due to these particles, is

A) zero.
B) positive.
C) negative.
D) impossible to determine based on the information given.