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.