using System;
using System.Collections.Generic;
using System.Text;

namespace Covariance
{
    class Base
    {}

    class Derived:Base
    {}

    class Program
    {
        static void Main(string[] args)
        {
            Base[] array = new Derived[5];
            array[0] = new Derived();
            array[1] = new Base(); //ArrayTypeMismatchException
        }
    }
}