16. Which of the following sets are functions from the set of first components to the set of second components?

Question

(a) {(b, a), (d, c), (a, e), (g, f)}

(b) {(a, b), (b, a), (c, c), (a, c)}

(c) {(b, a), (c, a), (b, b), (c, b)}

Answer 1

if for each first element, there is one and only one second element, we have a function.

I see only one set obeying that definition and its not b) or c).