Four charges, each equal to $-\mathrm{Q}$, are placed at the corners of a square and a charge $+q$ is placed at its centre. If the system is in equilibrium, the value of $\mathrm{q}$ is
(A) $(Q / 4)(1+2 \sqrt{2})$
(B) $-(\mathrm{Q} / 4)(1+2 \sqrt{2})$
(C) $-(Q / 2)(1+2 \sqrt{2})$
(D) $(Q / 2)(1+2 \sqrt{2})$