private void btnAdd_Click(object sender, EventArgs e)
 {
     if (cboCourse.SelectedValue == null || txtTitle.Text == "" || txtAnswerA.Text == "" || txtAnswerB.Text == "" || txtAnswerC.Text == "" || txtAnswerD.Text == "")
     {
         MessageBox.Show("请输入完整的题目信息!");
     }
     else if (ckbA.Checked == false && ckbB.Checked == false && ckbC.Checked == false && ckbD.Checked == false)
     {
         MessageBox.Show("请选择正确答案!");
     }
     else
     {
         string answer = "";
         if (ckbA.Checked == true)
         {
             answer += "A";
         }
         if (ckbB.Checked == true)
         {
             answer += "B";
         }
         if (ckbC.Checked == true)
         {
             answer += "C";
         }
         if (ckbD.Checked == true)
         {
             answer += "D";
         }
         try
         {
             SingleMultiProblem smp = new SingleMultiProblem(cboCourse.SelectedValue.ToString(), txtTitle.Text, txtAnswerA.Text, txtAnswerB.Text, txtAnswerC.Text, txtAnswerD.Text, answer);
             QuestionBll.AddmultiProblem(smp);
             MessageBox.Show("添加成功!");
             this.Close();
         }
         catch (Exception ee)
         {
             MessageBox.Show("添加失败!" + ee);
             throw;
         }
     }
 }