Which set of ordered pairs represents a function, and how does it represent that function?
a. {(2, –2), (1, 5), (–2, 2), (1, –3), (8, –1)}
b. {(3, –1), (7, 1), (–6, –1), (9, 1), (2, –1)}
c. {(6, 8), (5, 2), (–2, –5), (1, –3), (–2, 9)}
d. {(–3, 1), (6, 3), (–3, 2), (–3, –3), (1, –1)}