3. Which of these three sets of ordered pairs (x, y) represent functions of x? Explain your answer.
1. {(0, 0), (0, 1), (0, 2), (0, 3), (0,4)}
II. {(0, 0), (1, 1), (2, 2), (3, 3), (4,4)}
III. {(0, 0), (1, 0), (2, 0), (3, 0), (4, 0)}