The following is a correspondence one is
a.{(a,,,1)}
b.{(1,,,d)
c.{(1,,,b)
d.{(a,,,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. 

Check the internet ok that will

Bc equals mb that should be your answer