Find the Points of Inflection and Discuss the Concavity of the Function

Multiple Choice

Find the points of inflection and discuss the concavity of the function $f ( x ) = x \sqrt { x + 16 }$

A) no inflection points; concave up on $( - 16 , \infty )$
B) no inflection points; concave down on $( - 16 , \infty )$
C) inflection point at $x = 16$ ; concave up on $( - 16 , \infty )$
D) inflection point at $x = 0$ ; concave up on $( - 16,0 )$ ; concave down on $( 0 , \infty )$
E) inflection point at $x = 16$ ; concave down on $( - 16 , \infty )$