Which relation is a functiona) {(2.4), (2,-7) (2,11), (2,-15)}
b. {(0,-7), (4,-8), (0,-9,) (6,-10)}
c. {(-1.3), (5,3), (-6,7), (5,0)}
d. {(6.0), (-7,14), (-2,-5), (2.5)}?