1. Which set of relations is a function?
a. {(-1, 2), (-2, 0), (-1, 3)}
b. {(8, 3), (8, 4), (8, 5)}
c. {(0, 2), (2, 4), (4, 6), (6, 8)}
d. {(1, 5), (2, 7), (1, 6), (2, 5)}​