which set of ordered pairs does not represent a function?
A {(6,−1),(1,−9),(6,−3),(−6,−5)}
B {(5,5),(−5,2),(4,5),(1,1)}
C {(−5,4),(3,−9),(5,−7),(4,4)}
D {(4,1),(8,6),(−5,−1),(−3,−6)}