12. Given $x, y \in \mathbf{R}_{+}, x \neq 1, y \neq 1$, satisfying: $\log _{2} x=\log _{y} 16, x y=64$. Then $\left(\log _{2} \frac{x}{y}\right)^{2}$ is $(\quad$.
(A) $\frac{25}{2}$
(B) 20
(C) $\frac{45}{2}$
(D) 25
(E) 32