private void frmThemDauSach_Load(object sender, EventArgs e)
{
cbbTheLoai.DataSource = TheLoaiBUS.LayDSTheLoai();
cbbTheLoai.DisplayMember = "TenTheLoai";
cbbTheLoai.ValueMember = "MaTheLoai";
txtMaDauSach.Text = DauSachBUS.PhatSinhMa();
cbbTheLoai.SelectedItem = 0;
txtTenDauSach.Text = string.Empty;
}