A solid shaft of diameter of is replaced by a hollow shaft of the same material and length. The
outside diameter of hollow shaft is $\frac{2D}{\sqrt{3}}$ while the inside diameter is $\frac{d}{\sqrt{3}}$ . What is the ratio of the tensional stiffness of the hollow shaft to that of the solid shaft?
(a) $\frac{2}{3}$ (b) $\frac{3}{5}$ (c) $\frac{5}{3}$ (d) 2