What is the domain of the function below?

{0,2 3,1 5,2 8,4

The choices are the below that can be found elsewhere:

a. { 1, 2, 4 }

b. { 0, 3, 5, 8 }

c. { 0, 1, 2, 3, 4, 5, 8 }

d. { (0, 2), (3, 1), (5, 2), (8, 4) }

The answer is B because the domain is just the X-values of the ordered pairs and you cant repeat them.