Select the relation that IS a function. a. {(-6, -5), (3, 2), (10, 8), (3, 3)}
b. {(-2, -1), (5, -1), (16, 3), (-3, -9)}
c. {(5, 10), (-3, 10), (-3, -10), (4, 7)}
d. {(21, 11), (21, 10), (21, 9), (21, 8)}