using System;

using System.Globalization;

using System.Text;

using System.Text.RegularExpressions;

​

public abstract class Animal

{

    public string Name { get; set; }

}

​

public class Cat : Animal { }

​

public interface IAnimalShelter

{

    Animal GetAnimalForAdoption();

}

​

public class DogShelter : IAnimalShelter

{

    public Animal GetAnimalForAdoption()

    {

        throw new NotImplementedException();

    }

}

​

public class CatShelter : IAnimalShelter

{

    // Co-variant return type, where Cat : Animal

    public Cat GetAnimalForAdoption()

    {

        throw new NotImplementedException();

    }

}