1. Simplify $\sqrt{9 x^{2}-6 x+1}-(\sqrt{3 x-5})^{2}$, the result is ( ).
(A) $6 x-6$
(B) $-6 x+6$
(C) -4
(D) 4
$$
-1 . D \text {. }
$$

From $\sqrt{3 x-5}$, we get $3 x-5 \geqslant 0$. Then
$$
\begin{array}{l}
\sqrt{9 x^{2}-6 x+1}-(\sqrt{3 x-5})^{2} \\
=|3 x-1|-|3 x-5| \\
=(3 x-1)-(3 x-5)=4 .
\end{array}
$$