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";
}