16 If there exists a constant $m \in \mathbf{N}$, such that for all $n$ in the natural numbers, $a_{m+n}=a_{n}$, then $\left\{a_{n}\right\}$ is called a periodic sequence, and $m$ is called the period. Given that $\left\{q^{n}\right\}$ is a periodic sequence with the smallest positive period $m(m \geqslant 2)$, then ( )
A. When $m$ is odd, $q$ is any $m$-th root of 1
B. When $m$ is even, $q$ is any $m$-th root of 1 except 1
C. When $m$ is even, $q$ is any $m$-th imaginary root of 1
D. When $m$ is a prime number, $q$ is any $m$-th root of 1 except 1
16 D. $q^{m}=1$ and for any natural number $k$ smaller than $m$, $q^{k} \neq 1$. Therefore, A, B, and C are all incorrect.