public bool CheckAnswer(TextAnswer answer)
        {
            if (answer == null)
                throw new ArgumentNullException("answer", "answer is null.");

            return _answer.Equals(answer.AnswerText, StringComparison.InvariantCultureIgnoreCase);
        }
        public bool CheckAnswer(TextAnswer answer)
        {
            if (answer == null)
            {
                throw new ArgumentNullException("answer", "answer is null.");
            }

            return(_answer.Equals(answer.AnswerText, StringComparison.InvariantCultureIgnoreCase));
        }