3. Which set of ordered pairs represents a function?
A. {(a, 3), (b, 5), (d, 6), (d, 9)
B. {(a, 3), (b, 6), (C, 3), (c, 9)}
C.(a, 3), (b, 3), (C, 3), (d, 3}}
D. {(a, 5), (a, -9), (a,0), (a, 12)
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functinn?​