WebClient wc = new WebClient();
                wc.Encoding = System.Text.Encoding.UTF8;//定义对象的编码语言,此处或者是gb2312
                string xmlResult = wc.DownloadString(requestUrl);
                var jsonResult = GetResult(xmlResult);

        /// <summary>
        /// 解析返回的xml，取其中的结果
        /// </summary>
        /// <param name="xml"></param>
        /// <returns></returns>
        public static string GetResult(string xml)
        {
            var doc = new XmlDocument();
            doc.LoadXml(xml);
            var firstNode = doc.ChildNodes[1].InnerText;
            return firstNode;
        }