1. When $x=3$,
$$
\frac{\sqrt{x-2 \sqrt{2}}}{\sqrt{x^{2}-4 \sqrt{2} x+8}}-\frac{\sqrt{x+2 \sqrt{2}}}{\sqrt{x^{2}+4 \sqrt{2} x+8}}
$$

the value is ( ).
(A) 1
(B) $\sqrt{2}$
(C) $\sqrt{3}$
(D) 2
- 1. D.

When $x=3$,
$$
\begin{array}{l}
\text { Original expression }=\frac{\sqrt{(\sqrt{2}-1)^{2}}}{\sqrt{(3-2 \sqrt{2})^{2}}}-\frac{\sqrt{(\sqrt{2}+1)^{2}}}{\sqrt{(3+2 \sqrt{2})^{2}}} \\
=\frac{1}{\sqrt{2}-1}-\frac{1}{\sqrt{2}+1}=2 .
\end{array}
$$