var a = new A();
            var b = new B();

            a.DoSomething(); // result 'class A'
            b.DoSomething(); // reuslt : 'class B'
        }
    }

    class A
    {
        public void DoSomething()
        {
            Console.WriteLine("class A");
        }
    }
    class B : A
    {
        public void DoSomething()
        {
            Console.WriteLine("class B");
        }
    }