How Many Points of Inflection Does $f ( x ) = x ^ { 3 } e ^ { - x }$

How many points of inflection does $f ( x ) = x ^ { 3 } e ^ { - x }$ have?

A) 0
B) 1
C) 2
D) 3
E) 4
F) 5
G) 6
H) Infinitely many