If a rigid bar of length $l$ is pinned at one end and is released from rest in the horizontal position $(\theta = 0^{\circ})$, the magnitude of its angular acceleration is at maximum when

A. $\theta = 0^{\circ}$
B. $\theta = 90^{\circ}$
C. $\theta = 180^{\circ}$
D. $\theta = 0^{\circ}$ and $180^{\circ}$