private void btQuanLyDiem_Click(object sender, EventArgs e)
        {
            DanhSachLopHoc DSLH = new DanhSachLopHoc();

            DSLH.TopLevel = false;
            HienThi.Controls.Clear();
            HienThi.Controls.Add(DSLH);
            DSLH.Show();
        }
 private void btQuanLyDiem_Click(object sender, EventArgs e)
 {
     DanhSachLopHoc DSLH = new DanhSachLopHoc();
     DSLH.TopLevel = false;
     HienThi.Controls.Clear();
     HienThi.Controls.Add(DSLH);
     DSLH.Show();
 }