Function is a set of ordered pairs where there cannot be same x-values or repetitive domain in a set.
For example below below:
The following relation is a function since there are no same x-values in a set.
The following relation is not a function since there are same two x-values which is D = {1} or (1,1) and (1,2) both have same domain. Thus, not making the relation a function.
From the question, the relation is a function because in a set of ordered pairs, there aren't any same x-values.
Answer