17. If the complex number $z$ satisfies $z^{24}=1$, and $z^{6}$ is a real number, then there are $($ ) such complex numbers.
(A) 0
(B) 4
(C) 6
(D) 12
(E) 24
12.
17. D.
Notice that $z$ satisfying $z^{24}=1$ can be expressed as $z=\mathrm{e}^{\frac{n-i}{12}}(n \in \mathbf{N}$ and $0 \leqslant n<24)$.
Thus, $z^{6}=\mathrm{e}^{\frac{a x 1}{2}}$.
Therefore, $z^{6} \in \mathbf{R}$ is equivalent to $\frac{n}{2} \in \mathbf{Z}$, which means $n$ is even. Hence, $n$ is an even number between $0 \leqslant n<24$, and there are