Determine Where the Graph Of $f ( x ) = x ^ { 3 } - 3 x ^ { 2 } - 9 x + 1$

Determine where the graph of $f ( x ) = x ^ { 3 } - 3 x ^ { 2 } - 9 x + 1$ is concave down.

A) x > -1
B) x < -1
C) x < 1
D) x > 1