Help!! ASAP Is relation below a function? If it is a function, state its domain.

{(0,3),(2,-3),(1,8),(2,3)}

A. The relation is not a function.
B. The relation is a function. The domain is {0,1,2}.
C. The relation is a function. The domain is {-3,3,8}
D. The relation is a function. The domain is {-3,0,1,2,3,8}