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The graph of $y=f(x)$ is shown. At what values of $x$ in $[-6,6]$ does $f(x)$ appear to be non-differentiable?

$x=1$

$x=-2, \hspace{.1cm} x=1$

$x=-2, \hspace{.1cm} x=3$

$x=-2, \hspace{.1cm} x=1, \hspace{.1cm} x=3$