private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (comboBox1.SelectedIndex == 0)
            {
                MessageBox.Show("5 วินาที");
            }
            else if (comboBox1.SelectedIndex == 1)
            {
                MessageBox.Show("10 วินาที");
            }
            else if (comboBox1.SelectedIndex == 2)
            {
                MessageBox.Show("15 วินาที");
            }
        }