Look at this set of ordered pairs.

{ (4, 12), (7, 11), (3, 13), (11, 4), (7, 3)}

Which statement about the relation above is true?
a) It is not a function because the same values appear as both x and y-values.

b) It is not a function because the same x values have different y values.

c) It is a function because every x-value is unique.

d) It is a function because every x-value has only y-value.