如何将输出数据保存到XML文件Microsoft Visual Studio 2010

    public AdvertisementDAL selectAdvertisementLocation1(DateTime now, string gender)
    {
        AdvertisementDAL dal = null;
        string sql = "Select * From Advertisement Where @currentDate between StartDate AND EndDate AND TargetAudience = @gender AND Location = 1";
        SqlConnection conn = new SqlConnection(_connStr);
        SqlCommand cmd = new SqlCommand(sql, conn);
        cmd.Parameters.AddWithValue("@currentDate", now);
        cmd.Parameters.AddWithValue("@gender", gender);
        conn.Open();
        SqlDataReader dr = cmd.ExecuteReader();

        while (dr.Read())
        {
            _advertisementID = int.Parse(dr["AdvertisementID"].ToString());
            _location = int.Parse(dr["Location"].ToString());
            _image = dr["Image"].ToString();
            _targetAudience = dr["TargetAudience"].ToString();
            _url = dr["Url"].ToString();
            _onMouseOverText = dr["OnMouseOverText"].ToString();
            dal = new AdvertisementDAL(_advertisementID, _location, _image, _targetAudience,
                _url, _onMouseOverText);
        }
        conn.Close();
        dr.Close();
        dr.Dispose();
        return dal;
    }
    public AdvertisementDAL selectAdvertisement