public static function submit_choice_response_returns() {
        return new external_single_structure(
            array(
                'answers' => new external_multiple_structure(
                     new external_single_structure(
                         array(
                             'id'           => new external_value(PARAM_INT, 'answer id'),
                             'choiceid'     => new external_value(PARAM_INT, 'choiceid'),
                             'userid'       => new external_value(PARAM_INT, 'user id'),
                             'optionid'     => new external_value(PARAM_INT, 'optionid'),
                             'timemodified' => new external_value(PARAM_INT, 'time of last modification')
                         ), 'Answers'
                     )
                ),
                'warnings' => new external_warnings(),
            )
        );
    }