如何保存在xml文件上是不会被生成<>

                    XmlDocument XMLFile = new XmlDocument();
                    XMLFile.Load(HttpContext.Current.Server.MapPath(xml/thumbnails.xml));
                    XmlNode root= XMLFile.SelectSingleNode(Node);
                 
                    XmlNodeList xnl = XMLFile.GetElementsByTagName("thumbnails");
                   
                    if (xnl.Count != 0)
                    {
                        xnl[0].FirstChild.InnerText = "<thumbnail
filename=\"../upfile/Images/200912/20091204110027.jpg\" label=\"zcool1\" url=\"ProDetail.aspx?
Id=68&&MenuID=020103&&FirstNo=0201\">;";
                        XMLFile.Save(HttpContext.Current.Server.MapPath(Site));
                    }
<?xml version="1.0" encoding="utf-8"?>
<thumbnails>&lt;thumbnail filename="../upfile/Images/200912/20091204110027.jpg" label="zcool1"
url="ProDetail.aspx?Id=68&a