private void txtTK_HS_TextChanged(object sender, EventArgs e)
{
if (cbTK_HS.Text == "Mã")
{
dgvHocSinh.DataSource = tk.TK_Ma_HocSinh(txtTK_HS.Text);
}
else
{
dgvHocSinh.DataSource = tk.TKTenHocSinh(txtTK_HS.Text);
}
}