void NapLoaiDiem()
{
DataTable dt = new DataTable();
bus = new BUS_Diem();
dt = bus.showdata_LoaiDiem();
var item = new Dictionary <string, string>();
foreach (DataRow dr in dt.Rows)
{
item.Add(dr["MaLD"].ToString(), dr["MaLD"].ToString() + " - " + dr["TenLD"].ToString());
}
cbMaLD.DataSource = new BindingSource(item, null);
cbMaLD.DisplayMember = "Value";
cbMaLD.ValueMember = "Key";
}