The functions f(x)=√x^2+12x+36 and g(x)=x^3-12 are defined below. Which expression is equal to f(x) · g(x)? A.x^4-6x^3-12x+72 B.x^4-12x^3+6x-72 C.x^4+6x^3-12x-72 D. 7x^3-12x-72