The correct answer is C. Both A and B.
The maximum bending stress in a shaft subjected to a bending moment M and a torque T is given by
$$\sigma_{max} = \frac{{32{\text{M}}}}{{\pi {{\text{d}}^3}}}$$
where d is the diameter of the shaft.
The maximum shear stress in a shaft subjected to a bending moment M and a torque T is given by
$$\tau_{max} = \frac{{16{\text{T}}}}{{\pi {{\text{d}}^3}}}$$
Therefore, both A and B are correct.