Transcription: The three classes list, list-itter and phone-num are defined in one header file. They make up the linked list that is in a phone book object. You could modify the classes list and list-itter to provide the linked list for other applications. To do this you would simply define the data member first to be a pointer to an object of a different type and adjust the arguments of the member function insert. For simplicity the definition of list that is shown here is meant to be used specifically with the phone book class.