A function is a relation that pairs each element from set X (first number) to only one element of the set Y (second number)
For example let's say we have a set of X (3, 4) and a set of Y (6, 8)
The pairs would be (3,6), (4,8) now that's a function but if it were like this (3,6), (3,8) it wouldn't make a function since 3 is paired with both 6 and 8
The option that has requirements of a function is B.
