using System;

public class Program

{

    public static void Main()

    {

        Random rnd = new Random(Guid.NewGuid().GetHashCode());

        var boo = new Boo();

        boo.options[rnd.Next(boo.options.Length)].Foo();

    }

}

​

class Boo

{

    public A[] options;

    public Boo()

    {

        options = new A[]

        {

            new B(),

            new C(),

            new D(),

            new E()

        };

    }

}

​

class A

{

    public virtual void Foo() { Console.WriteLine(this.GetType().Name); }

}

​

class B : A{}

class C : A{}

class D : A{}

class E : A{}