private void button2_Click(object sender, EventArgs e)
{
frmSuaNgonNgu frm = new frmSuaNgonNgu();
frm.ShowDialog();
}
private void xoaSachToolStripButton_Click(object sender, EventArgs e)
{
frmSuaNgonNgu frmQLNN = new frmSuaNgonNgu();
frmQLNN.ShowDialog();
}