18. A group of five numbers are such that:
\begin{itemize}
\item their mean is 0
\item their range is 20
\end{itemize}
What is the largest possible median of the five numbers?
A 0\\
B 4\\
C $\quad 4 \frac { 1 } { 2 }$\\
D $\quad 6 \frac { 1 } { 2 }$\\
E 8\\
F 20\\