(1) Given $\theta \in\left[\frac{5 \pi}{4}, \frac{3 \pi}{2}\right]$, then $\sqrt{1-\sin 2 \theta}-\sqrt{1+\sin 2 \theta}$ can be simplified to ( ).
(A) $2 \sin \theta$
(B) $-2 \sin \theta$
(C) $-2 \cos \theta$
(D) $2 \cos \theta$
(1) $\mathrm{D}$ Hint: Since $\theta \in\left[\frac{5 \pi}{4}, \frac{3 \pi}{2}\right]$, so
$$
\begin{aligned}
& \sqrt{1-\sin 2 \theta}-\sqrt{1+\sin 2 \theta} \\
= & |\cos \theta-\sin \theta|-|\cos \theta+\sin \theta| \\
= & 2 \cos \theta .
\end{aligned}
$$