xn+1=(1+n2)xn+n4, for every positive integer n. If x1=−1, what is x2000?<spanclass=′latex−bold′>(A)</span>1999998<spanclass=′latex−bold′>(B)</span>2000998<spanclass=′latex−bold′>(C)</span>2009998<spanclass=′latex−bold′>(D)</span>2000008<spanclass=′latex−bold′>(E)</span>1999999