A unit square from one of the corners of a 8×8 chessboard is cut and thrown. At least how many triangles are necessary to divide the new board into triangles with equal areas?<spanclass=′latex−bold′>(A)</span>17<spanclass=′latex−bold′>(B)</span>19<spanclass=′latex−bold′>(C)</span>20<spanclass=′latex−bold′>(D)</span>21<spanclass=′latex−bold′>(E)</span>None of the above