using System;

public class Program

{

    public static void Main()

    {

        new A().WithLog();

        new B().WithLog();

        new C().WithLog();

        new D().WithLog();  

    }   

}

​

public class A {

    public override string ToString() => "A";

}

​

public class B : A {

    public new string ToString() => "B";

}

​

public class C : A {

    public override string ToString() => "C";

}

​

public class D : A {

    public string ToString() => GetType().Name;

}

​

public static class Ext {   

    public static void WithLog(this object o){

        Console.Write(o.ToString() + " " );

    }

}