Pick up the correct statement from the following :
A. The shear stress is maximum at the axis of the shaft subjected to a torque
B. The ratio of the polar moment of inertia and the radius of the shaft, is called the polar modulus of the shaft section.
C. Torsinal rigidity of the shaft is the torque that produces a twist of one radian in the length of the shaft
D. The angle of twist in a shaft subjected to a torque is inversely proportional to the twisting moment.