1. Simplify
$$
\sqrt{a+2+3 \sqrt{2 a-5}}-\sqrt{a-2+\sqrt{2 a-5}}
$$

The result is ( ).
(A) 1
(B) $\sqrt{2}$
(C) $\sqrt{3}$
(D) Depends on $a$
$-1 . \mathrm{B}$.
Let $\sqrt{2 a-5}=t(t \geqslant 0)$. Then $a=\frac{t^{2}+5}{2}$
Therefore, the original expression $=\sqrt{\frac{(t+3)^{2}}{2}}-\sqrt{\frac{(t+1)^{2}}{2}}$
$$
=\frac{(t+3)-(t+1)}{\sqrt{2}}=\sqrt{2} \text {. }
$$