Which of the following statements is valid? (where $\theta$ is the angular position, $\omega$ is the angular velocity, and $\alpha$ is the angular acceleration)

A. $\omega = \frac{d\alpha}{dt}$
B. $\alpha = \frac{d^2s}{dt^2}$
C. $\omega = \frac{d\theta}{dt}$
D. $\theta = \frac{d^2\alpha}{dt^2}$