Two hollow shafts of the same material have the same length and outside diameter. Shaft 1 has internal diameter equal to one of the outer diameter and shaft 2 has internal diameter equal to half of the outer diameter. If both the shafts are subjected to the same torque, the ratio of their twists $\theta_{1}/\theta _{2}$ will be equal to
(a) 16/81 (b) 8/27
(c) 19/27 (d) 243/256