Four particles, each of mass $M$ and equidistant from each other, move along a circle of radius $R$ under the action of their mutual gravitational attraction. The speed of each particle is
(A) $\sqrt{\frac{G M}{R}}$
(B) $\sqrt{2 \sqrt{2} \frac{G M}{R}}$
(C) $\sqrt{\frac{G M}{R}(1+2 \sqrt{2})}$
(D) $\frac{1}{2} \sqrt{\frac{G M}{R}(1+2 \sqrt{2})}$