{
            if (!checkBox1.Checked && checkBox2.Checked && checkBox3.Checked && checkBox4.Checked)
            {
                MessageBox.Show("必须选择一个答案");
            }
            else if (checkBox1.Checked)
            {
                checkBox2.Checked = false;
                checkBox3.Checked = false;
                checkBox4.Checked = false;
            }}
        private void checkBox2_CheckedChanged(object sender, EventArgs e)
        {
            if (!checkBox1.Checked && checkBox2.Checked && checkBox3.Checked && checkBox4.Checked)
            {
                MessageBox.Show("必须选择一个答案");
            }
            else if (checkBox2.Checked)
            {
                checkBox1.Checked = false;
                checkBox3.Checked = false;
                checkBox4.Checked = false;
            }}
        private void checkBox3_CheckedChanged(object sender, EventArgs e)
        {
            if (!checkBox1.Checked && checkBox2.Checked && checkBox3.Checked && checkBox4.Checked)
            {
                MessageBox.Show("必须选择一个答案");
            }
            else if (checkBox3.Checked)
            {
                checkBox1.Checked = false;
                checkBox2.Checked = false;
                checkBox4.Checked = false;
            }}
        private void checkBox4_CheckedChanged(object sender, EventArgs e)
        {
            if (!checkBox1.Checked && checkBox2.Checked && checkBox3.Checked && checkBox4.Checked) 《计算机网络》课程通用题库管理系统设计与实现(16):http://www.751com.cn/jisuanji/lunwen_183.html