Question

Which relations are functions and which are not functions?
Column A Column B
1.
{(3, 7), (3, 6), (5, 4),
(4, 7)}
2.
{(1, 5), (3, 5), (4, 6),
(6, 4)}
3.
{(2, 3), (4, 2), (4, 6),
(5, 8)}
4.
{(0, 4), (3, 2), (4, 2),
(6, 5)}
A.
function
B.
not a function
The letters are column B.