private void tàiLiệuToolStripMenuItem_Click(object sender, EventArgs e)
        {
            frmTAILIEU frm = new frmTAILIEU();

            frm.Show();
        }
 private void tàiLiệuToolStripMenuItem_Click(object sender, EventArgs e)
 {
     frmTAILIEU frm = new frmTAILIEU();
     frm.Show();
 }