The function ƒ(x) = {(1, 2), (2, 4), (3, 6), (4, 8)} can be represented in several other ways. Which is NOT a correct representation of the function ƒ(x)?

- other two options -
x is a natural number less than 5 and y is twice x

y = 2x and the domain is {1, 2, 3, 4}