D.
But to be accurate, this isn't even a function. For it to be a function, that -2 couldn't be without a pair. There should be a 1 on the right side. So, when you do f(x) = -2 + 3 you get 1. This set of numbers (-2, -1, 3 and 5) is called domain, and all elements of the function's domain has to have a pair in the codomain(2, 6, 8, 4). That doesn't happen, as we don't see a 1 there, that could be assigned to the - 2 of the domain.
But to be accurate, this isn't even a function. For it to be a function, that -2 couldn't be without a pair. There should be a 1 on the right side. So, when you do f(x) = -2 + 3 you get 1. This set of numbers (-2, -1, 3 and 5) is called domain, and all elements of the function's domain has to have a pair in the codomain(2, 6, 8, 4). That doesn't happen, as we don't see a 1 there, that could be assigned to the - 2 of the domain.