public ICritter Create(string type)
        {
            ICritter critter;

            switch (type)
            {
                case "Sheep":
                    critter = new Sheep();
                    break;
                case "Squirrel":
                    critter = new Squirrel();
                    break;
                default:
                    throw new ArgumentException("No such type of critter exists.");
            }

            return critter;
        }
        public ICritter Create(string type)
        {
            ICritter critter;

            switch (type)
            {
            case "Sheep":
                critter = new Sheep();
                break;

            case "Squirrel":
                critter = new Squirrel();
                break;

            default:
                throw new ArgumentException("No such type of critter exists.");
            }

            return(critter);
        }