<https://sachbaitap.com/bai-3-trang-18-sach-bai-tap-sbt-gdcd-6-c70a1949.html>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://sachbaitap.com/bai-3-trang-18-sach-bai-tap-sbt-gdcd-6-c70a1949.html>