Subject :IMO Class : Class 6
Group the given figures into three classes using each figure only once.
A 1, 5, 6; 2, 3, 4; 7, 8, 9
B 1, 4, 7; 2, 5, 8; 3, 6, 9
C 1, 2, 3; 4, 5, 8; 6, 7, 9
D 1, 3, 5; 2, 4, 8; 6, 7, 9
How can correct answer be A?