Given the two expressions below: 4x2 − 8 square root of x + 9 3y2 + 2x + 6 is the sum of the two expressions above a polynomial? why or why not? a. yes, because whenever two expressions are added, their sum will be a polynomial. b. yes, because both expressions are polynomials, so their sum will be a polynomial. c. no, because at least one of the expressions has two variables, so their sum will not be a polynomial. d. no, because one of the expressions is not a polynomial, so their sum will not be a polynomial.