Determine the Number of Turning Points of the Graph of the Function

Multiple Choice

Determine the number of turning points of the graph of the function.
$f ( x ) = 2 x ^ { 4 } + 4 x ^ { 2 } + 4$

A) Number of turning points: 3
B) Number of turning points: 1
C) Number of turning points: 5
D) Number of turning points: 2
E) Number of turning points: 4