Let X={−1,0,1,2} and Y={0,1,2,3,4}. A relation S from X to Y is defined by
S={(x,x2):x∈X}∪{(1,3)}.
Which of the following is true about S?
a) S is a function because each element of X is associated with some element of Y.
b) S is not a function because the input 1 corresponds to both 1 and 3.
c) S is not a function because (1,3) is not of the form (x,x2).
d) S is not a function because (−1,1) and (1,1) share the same output 1.