<https://secure.gravatar.com/avatar/9955cbad5d85b3da8fcef0fc42729c5a?s=96&amp;d=blank&amp;r=g>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://cursosonlineweb.com/propiedades-del-aluminio-2.html>