How many pairs of real numbers (x,y) are there such that x4+y4+2x2y+2xy2+2=x2+y2+2x+2y?<spanclass=′latex−bold′>(A)</span>6<spanclass=′latex−bold′>(B)</span>5<spanclass=′latex−bold′>(C)</span>4<spanclass=′latex−bold′>(D)</span>3<spanclass=′latex−bold′>(E)</span>2