Should must need to

http://learnenglishteens.britishcouncil.org/grammar/beginner-grammar/have-must-should-obligation-advice

https://www.thoughtco.com/must-have-to-and-need-to-in-english-4177288

https://www.businessenglish.com/grammar/modals-must-have-to-should-should-have.html?lang=spa