Let $y = f ( x )$ Be a Differentiable Function for Which the Graph of Its

Multiple Choice

Let $y = f ( x )$ be a differentiable function for which the graph of its derivative, ƒ ', is given below:
At what x-value(s) , if any, does the graph of ƒ have a vertical tangent?

A) x = 0 only
B) x = -3 only
C) x = 3 only
D) x = -3 and x = 3
E) None