Question

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)

Answer 1

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.