Organize the following set into inheritance hierarchies of classes. Draw the hierarchy. You may add additional classes to act as superclasses, if necessary. [Hint: use the isa rule]

\begin{tabular}{|l|l|l|} \hline Telephone & Phone Call & Phone Line \\ \hline Caller & Telephone Number & Call on Hold \\ \hline Conference Call & Voice Mail & Forwarded Call \\ \hline Digital Line & Call Waiting & Mobile Phone \\ \hline \end{tabular}