读取XML节点

    得到一个XML字符串，但不保存为.XML本地文件，但又要读取节点的值
  如：
 string param = "<?xml version=\"1.0\" encoding=\"utf-8\" ?>" +
                        "<CarClientTestRequest>" +
                         "<DateTime>2008-5-30 9:18:58</DateTime>" +
                         "<ClientPhone>15874019364</ClientPhone>" +
                         "<MessageType>139</MessageType>" +
                         "<State>000</State>" +
                         "<Parameter>00</Parameter>" +
                         "<TimeSpan>10</TimeSpan>" +
                        "</CarClientTestRequest>";string strClientPhone = 要得到ClientPhone的值？我写的在root.SelectSingleNode地方报错
            Stream ReStream = this.Request.InputStream;//接收传入的流数据
            StreamReader read = new StreamReader(ReStream, Encoding.UTF8);
            string content = read.ReadToEnd();            XmlDocument xmldoc = new XmlDocument();//实例化一个XmlDocument对像
            xmldoc.LoadXml(content);//加载为xml文档            XmlElement root = xmldoc.DocumentElement;
           string name = root.SelectSingleNode("CarClientTestRequest/ClientPhone").InnerText;