What is the product of the given polynomials?
a. x⁸ - 2x⁴y³ - 15y⁹
b. x⁸ - 2x⁴y³ - 15y⁶
c. x⁸ - 2x⁴y³ - 15y⁹
d. x⁸ + 2x⁴y³ - 15y⁶