Three Equal-Magnitude Point Charges of Varying Signs Are Placed at Three

Three equal-magnitude point charges of varying signs are placed at three of the corners of a square of side $d$ as shown in the figure. Which one of the arrows shown represents the direction of the net electric field at the vacant corner of the square?

A) $A$
B) $B$
C) $\mathrm { C }$
D) $\mathrm { D }$