static void Main()
    {
        // setup the metronome and make sure the EventHandler delegate is ready
        Metronome metronome = new Metronome();

        // wires up the metronome_Tick method to the EventHandler delegate
        Listener  listener  = new Listener(metronome);
        ListenerB listenerB = new ListenerB(metronome);

        metronome.Go();
    }