The moment of inertia of a solid sphere about an axis passing through centre of gravity is $\frac{1}{5} M R^{2}$; then its radius of gyration about a parallel axis at a distance $2 R$ from first axis is
(a) $5 R$
(b) $\sqrt{22 / 5} R$
(c) $\frac{5}{2} R$
(d) $\sqrt{12 / 5} R$