$$f ( x ) = \begin{cases} \frac { 2 } { x } & \text { for } x < - 1 \\ x ^ { 2 } - 3 & \text { for } - 1 \leq x \leq 2 \\ 4 x - 3 & \text { for } x > 2 \end{cases}$$
Let $f$ be the function defined above. At what values of $x$, if any, is $f$ not differentiable?\\
(A) $x = - 1$ only\\
(B) $x = 2$ only\\
(C) $x = - 1$ and $x = - 2$\\
(D) $f$ is differentiable for all values of $x$.