Select all the relations which represent a function.
- (1,3), (2,5), (2,7), (4,9) (1,3), (1,5), (1,7), (4,9) 0 (1,2), (2,5), (2,1), (4,5)
(1,3), (2,5), (3,7), (4,9) (1,3), (2,3), (3,3), (4,3)