/// <summary>
 /// 添加问题
 /// </summary>
 /// <param name="questions"></param>
 public void AddQuestionnaireQuestions(params Question[] questions)
 {
     foreach (var question in questions)
     {
         QuestionnaireQuestions.Add(QuestionnaireQuestion.CreateNew(this, question));
     }
 }
 /// <summary>
 /// 添加问题
 /// </summary>
 public void AddQuestionnaireQuestions(IEnumerable <Question> questions)
 {
     foreach (var question in questions)
     {
         QuestionnaireQuestions.Add(QuestionnaireQuestion.CreateNew(this, question));
     }
 }
        /// <summary>
        /// 创建问卷
        /// </summary>
        /// <param name="title"></param>
        /// <param name="questionDifficulty"></param>
        /// <returns></returns>
        public static Questionnaire CreateNew(string title, QuestionDifficulty questionDifficulty, IEnumerable <Question> questions)
        {
            var model = new Questionnaire
            {
                ID    = Guid.NewGuid(),
                Title = title,
                QuestionDifficulty     = questionDifficulty,
                CreatedStamp           = DateTime.Now,
                QuestionnaireQuestions = new List <QuestionnaireQuestion>()
            };

            foreach (var question in questions)
            {
                model.QuestionnaireQuestions.Add(QuestionnaireQuestion.CreateNew(model, question));
            }
            return(model);
        }