Answer:
D (0,4)
Step-by-step explanation:
You want to know an ordered pair that could be added to the given relation such that it remains a function.
A function cannot have any two ordered pairs that have the same x-value. The given relation has x-values {1, 2, 3, 4}, so none of these can be repeated if the relation is to remain a function.
The only choice with a different x-value is ...
D (0, 4)
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Additional comment
The set of x-values is the "domain" of the function. It cannot have any repeats. The set of y-values is the "range" of the function. Those values can be repeated.
A function that is "one-to-one" cannot have any repeated range values, either.
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