private void cb_tenmh_SelectedIndexChanged(object sender, EventArgs e)
{
QLHS_BUS bus = new QLHS_BUS();
DataTable dt = bus.LayMaMH(cb_tenmh.Text);
if (dt.Rows.Count > 0)
{
lb_mamonhoc.Text = dt.Rows[0]["MaMonHoc"].ToString();
}
}