private void btnExit_Click(object sender, EventArgs e)
        {
            this.Close();
            GV_QLDeThi frm = new GV_QLDeThi();

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

            frm.ShowDialog();
        }