Respuesta :

altavistard

Answer:

C

Step-by-step explanation:

Look for the case in which every input is unique (no repetitions).

A does not qualify, as 3 appears as an input twice.

B does not qualify, for the same reason

C qualifies (is a function), because all the inputs {1, 2, 3, 4} are unique.

D does not qualify (see A, above).