Let sk denote the sum of the <spanclass=′latex−italic′>k</span>th powers of the roots of the polynomial x3−5x2+8x−13. In particular, s0=3, s1=5, and s2=9. Let a, b, and c be real numbers such that sk+1=ask+bsk−1+csk−2 for k=2, 3, .... What is a+b+c?<spanclass=′latex−bold′>(A)</span>−6<spanclass=′latex−bold′>(B)</span>0<spanclass=′latex−bold′>(C)</span>6<spanclass=′latex−bold′>(D)</span>10<spanclass=′latex−bold′>(E)</span>26