public DataTable taocombonn(string mann) { clsdmngoaingu c = new clsdmngoaingu(); c.sc.Open(); string sql = "Select * from tbl_DMNgoaiNgu where mangoaingu ='" + mann + "'"; SqlCommand scmd = new SqlCommand(sql, c.sc); c.sda.SelectCommand = scmd; c.ds.Clear(); c.sda.Fill(c.ds, "DMNgoaiNgu"); c.sc.Close(); return(c.ds.Tables["DMNgoaiNgu"]); }