Select all that apply.
Which set of ordered pairs represent a function?

a. {(-7,0), (9,-1),(-4,3), (-4,-2)}
b. {(-1,3), (-10,-5),(-1,-6),(-1, -2)}
c. {(-9,-5), (6,-9), (6, -10), (6, 7)}
d. {(3,3), (3, -1),(3,5), (3,7)}
e. None of the above