public void DisplayOptions()
{
Console.WriteLine("1. Buy a Tiger for {0:C}", Tiger.GetPurchaseCost());
Console.WriteLine("2. Buy a Penguin for {0:C}", Penguin.GetPurchaseCost());
Console.WriteLine("3. Buy a Turtle for {0:C}", Turtle.GetPurchaseCost());
Console.WriteLine("4. Return");
}
