Final answer:
The domain of the function is all real numbers (-∞, ∞).
Step-by-step explanation:
The domain of a function refers to the set of all possible input values, or x-values, for which the function is defined. In this case, consider the function f(x) for 0 ≤ x ≤ 20. Since x can take any value between 0 and 20, inclusive, the domain of the function is the set of all real numbers in that range. Therefore, the correct answer is option A: (x) is all real numbers (-∞,∞).