MODAL VERBS REVISION

Check out the following links!

http://www.ecenglish.com/learnenglish/lessons/modal-verbs-1-permission-prohibition-obligation-no-obligation

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

https://learnenglish.britishcouncil.org/es/quick-grammar/modals-1

http://web2.uvcs.uvic.ca/elc/studyzone/410/grammar/410-modals-of-necessity-prohibition-and-permission1.htm

http://www.autoenglish.org/modalverbs/ModalsObligation.htm

https://elt.oup.com/student/solutions1stedition/ui_unit_page/unit7/grammar/exercise1?cc=br&selLanguage=pt

http://www.learnenglish-online.com/grammar/modals/tests/modalobligation.html

http://www.learnenglish-online.com/grammar/modals/tests/modalobligation2.html

http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-80352.php