Let $f ( x ) = \left\{ \begin{array} { c c } x ^ { 2 } & x \leq 0 \\- x ^ { 2 } & x > 0\end{array} \right.$

Multiple Choice

Let $f ( x ) = \left\{ \begin{array} { c c } x ^ { 2 } & x \leq 0 \\- x ^ { 2 } & x > 0\end{array} \right.$ Which of the following is true?

A) $f$ is discontinuous at 0.
B) $f$ does not have a derivative at 0.
C) $f$ has a corner at (0,0) .
D) $f$ has a has a horizontal tangent line at (0,0) .
E) $f$ has a vertical tangent line at (0,0) .