What is the domain of this relation? Is it a function?

Question

{(2, 7), (0, 3), (-4, 3)}
Select one:
a. {7, 3}; yes
b. {2, 0, -4}; no
c. {7, 3}; no
d. {2, 0, -4}; yes

Answer 1

(d)
no two pairs have the same 1st element.