Which relation is a function?


A:{(1, 1), (2, 4), (4,8), (8, 16),
(8,32)}
B: (8, -2) , ( 9, -2) , (10, -2) (11, -2), (12,3)
C: (2,-3), (2,-2), (2,-1), (2,0), (2,1)
D: (9,3) , (9,-3), (16,-4), (25,-5)