private void nguyênMẫuToolStripMenuItem_Click(object sender, EventArgs e)
 {
     if (phuongtien == null || phuongtien.IsDisposed)
     {
         phuongtien = new FrmPhuongTien();
     }
     phuongtien.ShowDialog();
 }
 private void danhSáchCácPhươngTiệnToolStripMenuItem_Click(object sender, EventArgs e)
 {
     FrmPhuongTien phuongtien = new FrmPhuongTien();
     phuongtien.Show();
 }