private void btHocKy_Click(object sender, EventArgs e)
        {
            DanhSachHocKy DSHK = new DanhSachHocKy();

            DSHK.TopLevel = false;
            HienThi.Controls.Clear();
            HienThi.Controls.Add(DSHK);
            DSHK.Show();
        }
 private void btHocKy_Click(object sender, EventArgs e)
 {
     DanhSachHocKy DSHK = new DanhSachHocKy();
     DSHK.TopLevel = false;
     HienThi.Controls.Clear();
     HienThi.Controls.Add(DSHK);
     DSHK.Show();
 }