public function clear_wrong(question_attempt $qa) {
        $response = $qa->get_last_qt_data();
        if (!$response) {
            return '';
        }
        $cleanresponse = $qa->get_question()->clear_wrong_from_response($response);
        $output = '';
        foreach ($cleanresponse as $name => $value) {
            $attr = array(
                'type' => 'hidden',
                'name' => $qa->get_qt_field_name($name),
                'value' => s($value),
            );
            $output .= html_writer::empty_tag('input', $attr);
        }
        return $output;
    }