https://www.theguardian.com/news/2017/aug/10/adele-vocal-cord-surgery-why-stars-keep-losing-their-voices?CMP=share_btn_fb
http://ideas.time.com/2013/08/16/singing-changes-your-brain/
https://www.nats.org/featured-article.html
http://kariragan.com/files/2008/08/Serious-about-Singing-Age-Appropriate-Repertoire-JOS-2015-.pdf
https://www.huffingtonpost.com/ruth-gerson/is-it-safe-for-children-t_1_b_851856.html