protected function choice_group($mform) {
        $options = array();
        for ($i = 1; $i <= $this->get_maximum_choice_group_number(); $i += 1) {
            $options[$i] = question_utils::int_to_letter($i);
        }
        $grouparray = array();
        $grouparray[] = $mform->createElement('text', 'answer',
                get_string('answer', 'qtype_gapselect'), array('size' => 30, 'class' => 'tweakcss'));
        $grouparray[] = $mform->createElement('select', 'choicegroup',
                get_string('group', 'qtype_gapselect'), $options);
        return $grouparray;
    }