private void laykhu()
{
DataTable dta = new DataTable();
dta = bd.LayKhu("A");
cbo_khuA.DataSource = dta;
cbo_khuA.ValueMember = "Khu";
cbo_khuA.DisplayMember = "Khu";
DataTable dtb = new DataTable();
dtb = bd.LayKhu("B");
cbo_KhuB.DataSource = dtb;
cbo_KhuB.ValueMember = "Khu";
cbo_KhuB.DisplayMember = "Khu";
DataTable dtc = new DataTable();
dtc = bd.LayKhu("C");
cbo_KhuC.DataSource = dtc;
cbo_KhuC.ValueMember = "Khu";
cbo_KhuC.DisplayMember = "Khu";
cbo_khuA.SelectedIndex = -1;
cbo_KhuB.SelectedIndex = -1;
cbo_KhuC.SelectedIndex = -1;
}