关于资料写入xml文件的问题

[symv]

我在写一个程序，将用户添写的资料写入xml文件里面，但是当我每次填写资料时，都把原来的资料给替换了，我该怎么办？
该函数如下：
public void CreateXmlFile(string name,string gender,string email,string department,string classid,string telephone,string address,string other,string note)
{
objXmlTextWriter.WriteStartElement("student");
objXmlTextWriter.WriteElementString("name",name);
objXmlTextWriter.WriteElementString("gender",gender);
objXmlTextWriter.WriteElementString("email",email);
objXmlTextWriter.WriteElementString("department",department);
objXmlTextWriter.WriteElementString("classid",classid);
objXmlTextWriter.WriteElementString("telephone",telephone);
objXmlTextWriter.WriteElementString("address",address);
objXmlTextWriter.WriteElementString("other",other);
objXmlTextWriter.WriteElementString("note",note);
objXmlTextWriter.WriteEndElement();
objXmlTextWriter.WriteEndDocument();
objXmlTextWriter.Flush();
objXmlTextWriter.Close();
}