Recall that for a relationship to be a function, it must satisfy that only one element of the range should be associated with an element of the domain.
Then, in our examples, we see that example a) cannot be a function because the number "4" of the domain (first number in the ordered pair of the form (x,y)) is associated with two different values: 5 in one case, and 1 in the other.
Example b) looks fine as an example of a function.
Example c) is NOT a function because the element 8 in the Domain is associated with 7 in the range and also with 4.
Example d) is Not a function either because the element 0 in the Domain is associated with -2 in one case and with -1 in another.
Only function shown is that of example b: (9,4),(-7,-4), (3,-5), (-3,5)
