using System;

public class Program

{

interface IStuffPerformer

{

  void PerformStuff(int amount);

}

​

public class GenericSoundPlayer : IStuffPerformer

{

   public virtual void PerformStuff(int amount)

   {

        Console.WriteLine("base");

   }

}

​

public class SoundEffectsPlayer : GenericSoundPlayer

{

   public override void PerformStuff(int amount)

   {

        Console.WriteLine("derived");

   }

}

​

public void Main()

{

  IStuffPerformer player = new SoundEffectsPlayer();

  // I treat it as IStuffPerformer

  // Which method will it call??

  player.PerformStuff(42);

}

}