<https://secure.gravatar.com/avatar/c2f4e0e0f28f2937551a9da922fdf728?s=96&amp;d=mm&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://pgddtthoaison.edu.vn/bai-11-trang-53-sgk-hinh-hoc-12/>