Group the following figures into three classes on the basis of identical properties:
1
1, 3, 9; 2, 4, 6; 5, 7, 8
2
1, 5, 9; 2, 4, 6; 3, 5, 7
3
1, 2, 5; 3, 6, 7; 4, 8, 9
4
1, 5, 9; 2, 3, 6; 4, 8, 7
Group the following figures into three classes on the basis of identical properties: