Question

Which relation is a function?

A.
{(1, 2); (2, 3); (3, 4); (2, 5)}

B.
{(1, 2); (3, 2); (3, 3); (4, 2)}

C.
{(1, 2); (1, 3); (1, 4); (1, 5)}

D.
{(1, 2); (2, 3); (3, 4); (4, 5)}

I think it's D

Answer 1

for a relation all the domain elements only have one image and all of them must be used.

Answer 2

@a7x_forever tell me what is the answer?