2. If $M=3 x^{2}-8 x y+9 y^{2}-4 x+6 y+13$ (where $x, y$ are real numbers), then the value of $M$ must be ( ).
(A) positive
(B) negative
(C) zero
(D) integer
2. A.

Notice that
$$
\begin{aligned}
M & =3 x^{2}-8 x y+9 y^{2}-4 x+6 y+13 \\
& =2(x-2 y)^{2}+(x-2)^{2}+(y+3)^{2} \geqslant 0,
\end{aligned}
$$

and $x-2 y, x-2, y+3$ these 3 numbers cannot be 0 at the same time, so, $M>0$.