using System;

​

public interface IPrint{

    void Print();

    void Print2();

    void Print3();

}

​

public class A : IPrint{

    public void Print(){

        Console.WriteLine("Print From A");

    }

    public void Print2(){

        Console.WriteLine("Print2 From A");

    }

    public virtual void Print3(){

    }

}

​

public class B : A{

    public void Print2(){

        //base.Print2();

        Console.WriteLine("Print2 From B");

    }

    public override void Print3(){

        Console.WriteLine("Print3 from B");

    }

}

public class Program

{

    public static void Main()

    {

        Console.WriteLine("Hello World");

        IPrint printer = new A();

        printer.Print();

        printer.Print2();

        Console.WriteLine("Hello World");

        printer = new B();

        printer.Print2();

        printer.Print3();

    }

}