Final answer:
The reasoning that Andrea could use to argue that multiplication of polynomials is closed is that when you multiply two polynomials, the result is always another polynomial.
Step-by-step explanation:
Andrea could argue that multiplication of polynomials is closed because when you multiply two polynomials, the result is always another polynomial. A polynomial is an algebraic expression that consists of variables, coefficients, and exponents, combined using addition, subtraction, and multiplication. When you multiply two polynomials, each term in one polynomial is multiplied by each term in the other polynomial, resulting in a new polynomial. This means that the set of polynomials is closed under multiplication.