using System;

​

public class A {

    public void Test() {

        Console.WriteLine("A"); 

    }

}

​

public class B : A {

    public new void Test() {

        base.Test();

        Console.WriteLine("B");

    }

}

​

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        var b = new B();

        Show(b);

    }

    public static void Show(A a) {

        a.Test();   

    }

}