Let $f(x)=\{\begin{array}{ccc}18-x^2,& \text{f}\text{o}\text{r}& x0\\ 18+x^2,& \text{f}\text{o}\text{r}& x>0\end{array}.$ Find each limit$.$

$($A$)\underset{x{0}^{+}}{lim}f(x)$

$($B$)\underset{x{0}^{-}}{lim}f(x)$

$($C$)\underset{x0}{lim}f(x)$

$($D$)f(0)$

$($A$)$ Select the correct choice and, if necessary, fill in the answer box to complete your choice.

A$.\underset{x{0}^{+}}{lim}f(x)=($Type an integer or a decimal.$)$

B$.$ The limit does not exist.

$($B$)$ Select the correct choice and, if necessary, fill in the answer box to complete your choice.

A$.\underset{?}{lim}f(x)=($Type an integer or a decimal.$)$

B$.$ The limit does not exist.

$($C$)$ Select the correct choice and, if necessary, fill in the answer box to complete your choice.

A$.\underset{vn}{lim}f(x)=($Type an integer or a decimal.$)$

B$.$ The limit does not exist

$($D$)$ Select the correct choice.

A$.$ f$(0)=$

B$.$ Thr function is not defined at x$=0$