3. Which relation is not a function?
A {(1,5), (2,6), (3,6), (4,7)}
B{(4,7, (2,1), (-3,6), (3,4)}
C {(-1,6), (1,3), (2,5), (1,7)}
D {(-1,2), (0,5), (5,0), (2,-1)}