1. If $\frac{2013 \times 2013}{2014 \times 2014+2012}=\frac{\mathrm{n}}{\mathrm{m}}$ (where $m$ and $n$ are coprime natural numbers), then the value of $m+n$ is ().
A. 1243
B. 1343
C. 4025
D. 4029
Analysis: Clever calculation.
$\frac{2013 \times 2013}{2014 \times 2014+2012}=\frac{2013^{2}}{2013^{2}+2 \times 2013+1+2013-1}=\frac{2013^{2}}{2016 \times 2013}=\frac{671}{672}, \mathrm{~m}+\mathrm{m}$ The value is $671+672=1343$. The answer is $B$.