using System;

​

    public class Base 

{ 

    public virtual string GetName()

    {

        return "Base";

    }

}

​

public class Derived : Base

{ 

    public override string GetName()

    {

        return "Derived";

    }

}

​

public static class Extensions

{

    public static string GetNameByExtension(this Base item)

    {

        return "Base";

    }

​

    public static string GetNameByExtension(this Derived item)

    {

        return "Derived";

    }

}

​

public static class Program   

{

    public static void Main()

    {

        Derived derived = new Derived();

        Base @base = derived;

​

        // Use the instance method "GetName"

        Console.WriteLine(derived.GetName()); // Prints "Derived"

        Console.WriteLine(@base.GetName()); // Prints "Derived"

​

        // Use the static extension method "GetNameByExtension"

        Console.WriteLine(derived.GetNameByExtension()); // Prints "Derived"

        Console.WriteLine(@base.GetNameByExtension()); // Prints "Base"

    }

}