<https://www.mastah.org/strontium-stronsium-sr-pengertian-sifat-dan-fungsi-kegunaan/#webpage>
<http://www.w3.org/1999/02/22-rdf-syntax-ns#type>
<https://www.mastah.org/strontium-stronsium-sr-pengertian-sifat-dan-fungsi-kegunaan/>