13. The graph of the function $f$ shown in the figure above has a vertical tangent at the point $( 2,0 )$ and horizontal tangents at the points $( 1 , - 1 )$ and $( 3,1 )$. For what values of $x , - 2 < x < 4$, is $f$ not differentiable?\\
(A) 0 only\\
(B) 0 and 2 only\\
(C) 1 and 3 only\\
(D) 0, 1, and 3 only\\
(E) 0, 1, 2, and 3\\