11. Let $x, y \in \mathbf{R}$, satisfy the equation
$$
x^{2}+y^{2}=10 x-6 y-34 \text {. }
$$

Then $x+y=(\quad)$.
(A) 1
(B) 2
(C) 3
(D) 6
(E) 8
11. B.
$$
\begin{array}{l}
\text { Given } x^{2}-10 x+25+y^{2}+6 y+9=0 \\
\Rightarrow(x-5)^{2}+(y+3)^{2}=0 \\
\Rightarrow x=5, y=-3 \Rightarrow x+y=2 \text {. }
\end{array}
$$