Final answer:
The domain of the function is all non-negative integers that are multiples of 9.
Step-by-step explanation:
The domain of a function represents the set of values for which the function is defined. In this case, the function is c(x) = 200 + 16x, where x is the number of complete products manufactured. The function is defined for all non-negative integers, since the number of complete products cannot be negative. Therefore, the correct answer is C. all non-negative integers that are multiples of 9.