Question

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

can someone give me the answer