private void btnNopBai_Click(object sender, EventArgs e)
        {
            DialogResult kq = MessageBox.Show("Bạn có chắc muốn nộp bài thi?", "Thông báo", MessageBoxButtons.YesNo, MessageBoxIcon.Information);

            if (kq == DialogResult.Yes)
            {
                ChonDapAn();
                double soDiem    = TinhDiem();
                double soCauDung = SoCauDung();
                if (loai == "ThiThu")
                {
                    hocSinhBUS.AddKetQuaThiThu(hocSinhLogin.MaHocSinh, maDeDuocChon, maKhoiHS, soDiem);
                }
                if (loai == "Thi")
                {
                    string maDeVaKhoiTrongKyThi = dsCauHoiThi[0].MaDeVaKhoiTrongKyThi;
                    hocSinhBUS.AddKetQuaThi(hocSinhLogin.MaHocSinh, maDeVaKhoiTrongKyThi, soDiem);
                }
                HetGioForm hetGio = new HetGioForm(hocSinhLogin, stopTimer, soDiem, soCauDung, phut, giay, loai);
                this.Hide();
                hetGio.ShowDialog();
                this.Close();
                Application.Exit();
            }
            else
            {
                return;
            }
        }
        private void timer1_Tick(object sender, EventArgs e)
        {
            giay -= 1;
            if (giay < 0)
            {
                phut -= 1;
                giay  = 59;
            }

            lbTimerPhut.Text = phut.ToString();
            lbTimerGiay.Text = giay.ToString();

            if (phut < 0)
            {
                if (loai == "ThiThu")
                {
                    ChonDapAn();
                    double soDiem    = TinhDiem();
                    int    soCauDung = SoCauDung();
                    hocSinhBUS.AddKetQuaThiThu(hocSinhLogin.MaHocSinh, maDeDuocChon, maKhoiHS, soDiem);
                    HetGioForm hetGio = new HetGioForm(hocSinhLogin, stopTimer, soDiem, soCauDung, phut, giay, loai);
                    this.Hide();
                    hetGio.ShowDialog();
                    this.Close();
                    Application.Exit();
                }

                if (loai == "Thi")
                {
                    ChonDapAn();
                    double soDiem               = TinhDiem();
                    int    soCauDung            = SoCauDung();
                    string maDeVaKhoiTrongKyThi = dsCauHoiThi[0].MaDeVaKhoiTrongKyThi;
                    hocSinhBUS.AddKetQuaThi(hocSinhLogin.MaHocSinh, maDeVaKhoiTrongKyThi, soDiem);
                    HetGioForm hetGio = new HetGioForm(hocSinhLogin, stopTimer, soDiem, soCauDung, phut, giay, loai);
                    this.Hide();
                    hetGio.ShowDialog();
                    this.Close();
                    Application.Exit();
                }
            }
        }