Answer:
{(1, 2), (3, 2), (5, 7)}
Explanation:
A function has a one to one correspondence
Each x can go to only 1 y value
{(1, 2), (3, 2), (5, 7)} function
{(3, 5), (-1, 7), (3, 9)} 3 goes to more than 1 y value
{(1, 2), (1, 4), (1, 6)} 1 goes to more than 1 y value