# The function $f(x)=\left\{\begin{array}{1 1}1&x\leq -1\\|x|&-1< x < 1\\0&x\geq 1\end{array}\right.$
$\begin{array}{1 1}(a)\;\text{differentiable for all x}\\(b)\;\text{f is continuous everywhere}\\(c)\;\text{f is differentiable at x=-1}\\(d)\;\text{f is continuous at x=-1}\end{array}$