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