Determine whether the relation is a function.
(0, 1) (5, 6) (7, 9) (8, 9)
A. Not a function, there is not a unique y-value for each x-value
B. Not a function, there is not a unique x-value for each y-value
C. Function, there is a unique x-value for each y-value
D. Function, there is a unique y-value for each x-value