Answer:
{(1, 1), (1, 3), (2, 3), (3,4)} is not a function.
Step-by-step explanation:
The lists are:
a) {(1, 1), (2, 3), (3, 4), (4,5)}
b) {(1, 1), (2, 2), (3, 3), (4,4)}
c) {(1, 1), (3, 1), (4,2), (5, 3) }
d) {(1, 1), (1, 3), (2, 3), (3,4)}
Firs, let's define what is a function.
A function is a relationship that maps elements from a set (the domain, is the set of the inputs) into elements of another set (the range, the set of the outputs) such that each element of the domain can be mapped into only one element of the range.
Then the list where we have the same input mapped into two different outputs, will not be a function.
Where in a ordered pair (x, y)
x is the input, and y is the output.
In this case, the list that is not a function is:
d) {(1, 1), (1, 3), (2, 3), (3,4)}
because we have the input x = 1, mapped into two different outputs.
, 
, and so on.