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><thumbnail filename="../upfile/Images/200912/20091204110027.jpg" label="zcool1"

url="ProDetail.aspx?Id=68&&MenuID=020103&&FirstNo=0201"></thumbnails>