Define a class Controller with four virtual functions on(), off(), set_level(int), and show(). Derive at least two classes from Controller. One should be a simple test class where show() prints out whether the class is set to on or off and what is the current level. The second derived class should somehow control the line color of a Shape; the exact meaning of "level" is up to you. Try to find a third "thing" to control with such a Controller class.