public static string LetterTransformationNum(string answer, int type)
        {
            string num = "";
            if (type == 1 || type == 2) //(1和2代表单选和多选)
            {
                var str = answer; //去答案
                str = TrimAllHtmlTag(str).Replace("】", "");
                StringBuilder sp = new StringBuilder();
                for (int i = 0; i < str.Length; i++)
                {
                    if (str[i] >= 'A' && str[i] <= 'G')
                    {
                        sp.Append((char)str[i] - 'A');
                    }
                    else
                    {
                        sp.Append(str[i]);
                    }
                }
                object numanswer = sp.ToString();
                num = Convert.ToString(numanswer);
            }

            num = String.Join(",", (from c in num select c + "").ToArray()); //加，

            string answerValue = "[" + num + "]";
            return answerValue;
        }

 public static string TrimAllHtmlTag(string str)
        {
            string reg = "<([^>]+?)>";
            return Regex.Replace(str, reg, "").Trim();
        }