Answer
d) is correct.
Work Step by Step
Because angular speed $\omega$ is constant, angular acceleration $\alpha=0rad/s^2$
We have $a_T=r\alpha $. Because $\alpha=0$, $a_T=0rad/s^2$
We have $a_c=r\omega^2$. Because $\omega\ne0$ and $r\ne0$, it follows that $a_c\ne0$
d) is correct.
