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"]);
}