private void main(string path)
        {
            XmlNodeList N2;

            Essay_exam_withSentence_reader essay_exam_withSentence_reader = new Essay_exam_withSentence_reader();
            N2 = essay_exam_withSentence_reader.question_reader(path);

            Essay_exam_answer_writer essay_exam_answer_writer = new Essay_exam_answer_writer();
            essay_exam_answer_writer.setpath(".\\xml\\exam_answer.xml");

            Essay_AE_find_sentence essay_AE_find_sentence = new Essay_AE_find_sentence();

            foreach(XmlNode n2 in N2)
            {
                XmlDocument xmldocument = new XmlDocument();
                XmlNode new_n2 = xmldocument.ImportNode(n2, true);
                List<string> Answer;
                Answer = essay_AE_find_sentence.findanswer(new_n2);
                essay_exam_answer_writer.write_answer(new_n2, Answer);
            }

            essay_exam_answer_writer.save();

            MessageBox.Show("finish AE");
        }
        public List<string> findanswer(XmlNode N2)
        {
            List<string> Answer = new List<string>();
            Essay_exam_withSentence_reader essay_exam_withSentence_reader = new Essay_exam_withSentence_reader();

            XmlNodeList KeyList = essay_exam_withSentence_reader.keylist_reader(N2);
            XmlNodeList sentenceList = essay_exam_withSentence_reader.sentences_reader(N2);

            return Answer;
        }