Which relations are functions and which are not functions?
column a column b
1.
{(2, 2), (4, 4), (6, 6),
(8, 8)}
2.
{(0, 3), (3, 5), (5, 6),
(8, 4)}
3.
{(1, 2), (3, 3), (4, 8),
(6, 3)}
4.
{(3, 4), (5, 2), (5, 6),
(7, 3)}

a.
function
b.
not a function

A) A
B) A
C)A
D) B
Reason I know this is because if we look at the x number in all of these, if 2 are the same (like 2,6 and 2,4) then its a non function.
But if none of the x =the same value its a function.
Same goes for B
C 
and now D, is a non function because out X's:
3
5
5
7
5 was repeated so it's a nonfunction.
Got it?

(I also just took this test XD)