1. The number of integer pairs $(m, n)$ that satisfy the equation $\frac{2011}{m}+\frac{1}{n}=1$ is ( ).
(A) 2
(B) 3
(C) 5
(D) 6
-1. B.
The original equation can be transformed into
$$
\begin{array}{l}
(m-2011)(n-1)=2011 \text { (prime). } \\
\text { Also, } 2011=1 \times 2011=(-1) \times(-2011) \text {, } \\
m \neq 0,
\end{array}
$$

Then $m-2011$ can take three values $\pm 1,2011$, and accordingly $n-1$ also has three integer values.