using System;

using System.Collections.Generic;

public class Program

{

    public static void Main()

    {

        List<A> basetypelist = new List<A>();

        basetypelist.Add(new B());

        basetypelist.Add(new A());

        foreach(var a in basetypelist)

        {

            Console.WriteLine(a.GetType());

        }

    }

}

public class A

{

}

public class B : A

{

}