Hi there.
The answer is B choice.
Explanation:
A function is a set of relation with no repetitive domains.
Here is an example of being a function and relation.
~ Function ~
Given the relation r = {(1,1),(2,4),(3,9),(4,16)}
As you see, there are no repetitive domains. Thus this relation is a function.
~ Relation ~
Given r = {(1,1),(1,2),(2,6),(3,28)}
As you see, there are the repetitive domains in this relation. And that is x = 1. Therefore, this relation is not a function but only a relation.
