//将学生选择的答案记录到studentAnswer[]中
        private void radioBtA_Click(object sender, EventArgs e)
        {
            QuizHelper.studentAnswers[QuesIndex] = Convert.ToString(((RadioButton)sender).Tag);
        }

        private void AnswerCard_Load(object sender, EventArgs e)
        {
            countdown.Start();//启动倒计时
            int index = 0;
            foreach (Control item in this.Controls)
            {
                if (item is Label)//如果是标签
                {
                    index = Convert.ToInt32(item.Tag);
                    if (index != -1)
                    {
                        item.Text = QuizHelper.studentAnswers[index];
                    }
                }
            }
        }