| Modals of obligation |

Vídeo com explicação: https://www.youtube.com/watch?v=QTu03baHmWw

Link 1: http://baladre.info/english/sedaviwebfront/mustshould.htm

Link 2: http://www.englishexercises.org/makeagame/viewgame.asp?id=6270

Link 3: https://elt.oup.com/student/englishfile/intermediate/a_grammar/file03/nef_int_grammar03_a01?cc=global&selLanguage=en

Link4:

http://www.englishforeveryone.org/PDFs/Modal%20Auxiliary%20verbs%20-%20Must%20and%20Have%20to.pdf