For every real x, the polynomial p(x) whose roots are all real satisfies p(x2−1)=p(x)p(−x). What can the degree of p(x) be at most?<spanclass=′latex−bold′>(A)</span>0<spanclass=′latex−bold′>(B)</span>2<spanclass=′latex−bold′>(C)</span>4<spanclass=′latex−bold′>(D)</span>There is no upper bound for the degree of p(x)<spanclass=′latex−bold′>(E)</span>None