More Nodes Higher Energy No nodes One node (x=$) Lowest Energy Next Lowest Energy Two nodes(x=号，) Three nodes(k=号，是，) Higher Energy Even Higher Energy Ⅱ-12More Nodes = Higher Energy No nodes Lowest Energy Next Lowest Energy Higher Energy Even Higher Energy One node (x= ) d 2 Two nodes (x= , ) d 3 2d 3 Three nodes (x= , , ) d 4 3d 4 d 2 II-12