The graph of function $h$ is given below. It has a vertical tangent at the point $(1,-4)$ and a horizontal tangent at the point $(-3,4)$.
**Select all the $x$-values for which $h$ is not differentiable.**
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![Graph](web+graphie://ka-perseus-graphie.s3.amazonaws.com/bbccbb212dc6d838837a99f1212ce95397daa8d0)