1. Which function is not one-to-one?
a. {(0, 1), (1, 2), (2, 3), (3, 4)}
b. {(0, 0), (1, 1), (2, 2), (3, 3)}
c. {(0, 1), (1, 0), (2, 3), (3, 2)}
d. {(0, 1), (1, 0), (2, 0), (3, 2)}