Which of the following correctly identifies the set of outputs?
a. {–3, –1, 3, 4}
b. {–5, –2, –1, 4}
c. {(–5, 4), (–2, –1), (–1, 3), (4, –3)}
d. {(4, –5), (–1, –2), (3, –1), (4, –3)}