how to resolve this error

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C#

var data = doc.Element("testes").Elements("teste");


getting error for this line at element

Error 1 'System.Xml.XmlDocument' does not contain a definition for 'Element' and no extension method 'Element' accepting a first argument of type 'System.Xml.XmlDocument' could be found (are you missing a using directive or an assembly reference?)

code:

XmlDocument doc = new XmlDocument();
            doc.Load(@"C:\Sampledata.xml");
            var data = doc.Element("testes").Elements("teste");

            Dictionary<string, string> hash = new Dictionary<string, string>();

            var result = from d in data
                         select new Dictionary<string, string>()
             { 
                { "sernum", (string)d.Attribute("sernum") },
                 { "rectime", (string)d.Attribute("rectime") },
                 { "area", (string)d.Attribute("area") },
                 { "machine", (string)d.Attribute("machine") },
                 {"cell",(string)d.Attribute("cell")}
             };

            foreach (var item in result)
            {
                foreach (var y in item)
                {
                    hash.Add(y.Key, y.Value);
                }
            }