using System;
using System.Collections.Generic;
public interface IHuman { void Speak(); }
public class Japanese : IHuman { public void Speak() { System.Console.WriteLine("私は日本人です。"); } }
public class European : IHuman { public void Speak() { System.Console.WriteLine("I am European."); } }
public class Program
{
    public static void Main()
    {
        List<IHuman> humans = new List<IHuman> { new Japanese(), new European() };
        humans.ForEach(x => x.Speak());
    }
}