Which set of ordered pairs represents y as a function of x? Group of answer choices

{(0, 0), (1, 1), (1, 0), (2, 1)}

{(2, -1), (4, -2), (6, -3), (8, -4)}

{(1, -5), (1, 5), (2, -10), (2, -15)}

{(3, 3), (3, 4), (4, 3), (4, 4)}

{(2, -1), (4, -2), (6, -3), (8, -4)}

In this relation, each point has a unique x coordinate. None of the x coordinates repeat themselves.

For something like choice A, we have x = 1 repeated. The input x = 1 leads to multiple outputs (y = 1 and y = 0 simultaneously).

The same situation happens in choice C also. This time x = 1 and x = 2 repeat themselves.

Choice D has x = 3 and x = 4 repeat themselves.

A function is only possible if each x input leads to exactly one y output.