static void Main()
        {
            Course c = new Course("Angular", 15, 2000);

            c.Print();  // Print() of Course

            c = new OnlineCourse
                    ("Python", "http://www.xyz.com/2343", 40, 5000);
            c.Print(); // Print() of OnlineCourse
        }
 static void Main()
 {
     Course       c1 = new Course("Angular", 15, 2000);
     OnlineCourse c2 = new OnlineCourse
                           ("Python", "http://www.xyz.com/2343", 40, 5000);
 }