/// <summary>
        /// 根据单元获取题库信息
        /// </summary>
        /// <param name="unitid"></param>
        /// <returns></returns>
        public string GetQuestion(int unitid, string tp, string qn)
        {
            List <BackQuestionBank> list = question.GetQuestionById(unitid, tp, qn);

            return(Newtonsoft.Json.JsonConvert.SerializeObject(list));
        }