Which of the following describes the graph of the equation (x \plus{} y)^2 \equal{} x^2 \plus{} y^2?<spanclass=′latex−bold′>(A)</span> the empty set<spanclass=′latex−bold′>(B)</span> one point<spanclass=′latex−bold′>(C)</span> two lines<spanclass=′latex−bold′>(D)</span> a circle<spanclass=′latex−bold′>(E)</span> the entire plane