protected static function times() {
        return array(
            self::DURING            => get_string('reviewduring', 'quiz'),
            self::IMMEDIATELY_AFTER => get_string('reviewimmediately', 'quiz'),
            self::LATER_WHILE_OPEN  => get_string('reviewopen', 'quiz'),
            self::AFTER_CLOSE       => get_string('reviewclosed', 'quiz'),
        );
    }