1. Which relation is not a function?
A (7,3), (7,6), (7,9), (7, 12), (7, 15)
B (-4, 6), (0,6), (7,6), (4,6), (-7,6)
C (4, 1), (8,2), (12,3), (16,4), (20,4)
D (1,3), (3,5), (5,7), (7, 9), (9, 1)