Answer: The correct option is (D) (x - 3).
Step-by-step explanation: Given that a polynomial function has a zero at x = 3.
We are to select the correct expression that must be a factor of the polynomial.
<em><u>FACTOR THEOREM : </u></em> The theorem states that if x = a is a zero of a polynomial p(x), then (x - a) will be a factor of the polynomial p(x).
In case of our given polynomial, since x = 3 is a zero of the polynomial, so by factor theorem, we can say that
(x - 3) is a factor of the given polynomial.
Thus, the required factor is (x - 3).
Option (D) is CORRECT.