若集合 $A=\{x \mid \sin 2 x=1\}, B=\left\{y \left\lvert\, y=\frac{\pi}{4}+\frac{k \pi}{2}\right., k \in Z\right\}$, 则下列结论正确的是
$\text{A.}$ $A \cup B=B$
$\text{B.}$ $C_R B \subseteq C_R A$
$\text{C.}$ $A \cap B=\varnothing$
$\text{D.}$ $C_R A \subseteq C_R B$