Final answer:
Marco's reasoning is partially correct; a relation where inputs have unique outputs is a function, but repeating output values do not define whether a relation is a function or not.
Step-by-step explanation:
Marco's explanation about how to determine if the relation in an input-output table is a function can be summarized as follows: In mathematics, a function is defined as a relation where each input is associated with a unique output. This means that even though an output value can repeat, what is crucial is that each input value is paired with one output value only. If an input has multiple different outputs, then the relation is not a function. Therefore, Marco's assertion is partially correct, but his focus on repeated output values is misleading. Instead, Devon should check for inputs having multiple different outputs to determine if the relation is not a function. The correct reasoning is aligned with option (d) where Marco is incorrect; a function can indeed have repeated output values for different inputs.