Answer the following questions for the function $$f(x) = x \sqrt{x^2 + 4}$$ defined on the interval $[ -5, 4 ]$.

A. $f(x)$ is concave down on the interval to
B. $f(x)$ is concave up on the interval to
C. The inflection point for this function is at $x=$
D. The minimum for this function occurs at $x=$
E. The maximum for this function occurs at $x =$