Question $2\mathrm{.}2\mathrm{.}0\mathrm{.}4\mathrm{.}15.$ Determine the values of a for which $\underset{xa}{lim}f(x)$ does not exist, $f(x)=\{\begin{array}{ccc}{e}^x& if& x0\\ x-1& if& 0=1\end{array}$

A$.\underset{xa}{lim}f(x)$ exists for all values of $a.$

B$.a=1$

C$.a=0$

D$.a=1$ and $a=0$