Hello!
Remember: to be a function, each value of the domain must have only one range.
Knowing it, let's analyze the options:
A. {(1,2), (2,3), (3,4), (4,5)}
okay, all elements in the domain just have one range.
B. {(4,1), (5,1), (6,1), (7,1)}
okay, all elements in the domain just have one range.
C. ((4,5), (4,2), (5,4), (2,4)}
Ops! When x = 4 in the domain, there are two different results in the range, and it cannot happen.
Answer:
Alternative C is not a function.