private void loadComboBoxes()
        {
            cbHangXe.DataSource    = XeBUS.LoadHangXe();
            cbHangXe.DisplayMember = "TenHangXe";
            cbHangXe.ValueMember   = "MaHangXe";

            cbLoaiXe.DataSource    = XeBUS.LoadLoaiXe();
            cbLoaiXe.DisplayMember = "TenLoaiXe";
            cbLoaiXe.ValueMember   = "MaLoaiXe";

            cbNCC.DataSource    = XeBUS.LoadNCC();
            cbNCC.DisplayMember = "TenNhaCungCap";
            cbNCC.ValueMember   = "MaNhaCungCap";
        }