The following is a correspondence one is

A.{ (a, 1), (b, 1), (c, 1) }

B.{ (1, a), (2, c), (3, d)

C.{ (1, b), (2, c), (3, b)

D.{ (a, b), (c, d), (b, d)

I'm assuming you meant to say "one-to-one"

If so, then the answer would be choice B.{ (1, a), (2, c), (3, d)

This is because each input leads to a different output and the outputs are different all across the board. In the other choices, the outputs repeat themselves at least twice which means they are not one-to-one functions.