If f(x)=x^3 and g(x)=x^2, and x is a natural number, what CANNOT the answer be for f(g(x))?  Choose the correct choice from the following:
A) 1
B) 64
C) 729
D) 512
E) 4096
512 is not a possible answer because 512 is equal to 8 cubed, because x must first be squared by g(x) before it is cubed by f(x), and 8 is not a perfect square, therefor there is no natural number that can be used to make f(g(x))=512. The answer is 512.
<result>D</result>
If f(x)=x^3 and g(x)=x^2, and x is a natural number, what CANNOT the answer be for f(g(x))?