grade 7: modal auxiliaries

 https://www.grammarbank.com/must-vs-need-to-have-to.html

https://www.montsemorales.com/gramatica/ObligProhib.htm

https://test-english.com/grammar-points/a2/have-to-dont-have-to-must-mustnt/

https://test-english.com/grammar-points/b1/have-to-must-should/

https://www.englishclub.com/grammar/verbs-modals-have-to-must-not-quiz.htm