public function getFirstSentence($number = 1, $i = null)
    {
        $wiki_api = sprintf($this->base_api . 'action=query&prop=extracts&exsentences=%d&explaintext=&exsectionformat=plain&pageids=%s', intval($number), $this->getId());
        $json_wapi = json_decode(file_get_contents($wiki_api), true);

        return $this->get_list_or_item($json_wapi['query']['pages'], 'extract', $i);
    }