Let a,b, and c be positive integers with a≥b≥c such that
\begin{align*} a^2-b^2-c^2+ab&=2011\text{ and}\\
a^2+3b^2+3c^2-3ab-2ac-2bc&=-1997\end{align*}
What is a?<spanclass=′latex−bold′>(A)</span>249<spanclass=′latex−bold′>(B)</span>250<spanclass=′latex−bold′>(C)</span>251<spanclass=′latex−bold′>(D)</span>252<spanclass=′latex−bold′>(E)</span>253