Let a=112+322+532+⋯+200110012 and b=312+522+732+⋯+200310012. Find the integer closest to a−b.<spanclass=′latex−bold′>(A)</span>500<spanclass=′latex−bold′>(B)</span>501<spanclass=′latex−bold′>(C)</span>999<spanclass=′latex−bold′>(D)</span>1000<spanclass=′latex−bold′>(E)</span>1001