Which of these relations are​ functions? a
(4,4), (5,4),​ (6,4), (7,4),​ (8,4)
b
​(4,4), (5,6),​ (6,8), (6,10),​ (7,12)
c
​(7,33), (8,30),​ (9,27), (10,24),​ (11,21)
d
(6,9), (7,19),​ (8,29), (8,39),​ (9,49)

pls help me

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