A relation is a function if for each x-value there is **exactly** one y-value associated with it.

In the first choice, the relation has 2 y-values for the same x-value of 1. It is not a function.

In the second choice, every x-value has only 1 y-value. This is a function.

In the third choice, there are 2 y-values for the x-value of 1. This is not a function.

**Therefore, the correct choice is the second option or the relation {(1,4), (2, 4), (4, 4), (0, 4)} is a function.**

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