In a correspondence diagram, which visual clue indicates that the underlying relation fails to be a function?

• A. Every input has exactly one outgoing arrow, but some outputs might have no incoming arrows
• B. Some output point has two or more arrows leaving it, pointing to different inputs
• C. There exists a circular arrow from an input back to itself, showing reflexivity in the mapping
• D. Some input point has two or more arrows leaving it, pointing to different outputs

Answer: (D)