http://www.learnenglish-online.com/grammar/modals/tests/modaladvice.html http://www.learnenglish-online.com/grammar/modals/tests/modaladvice2.html
https://www.englisch-hilfen.de/en/exercises/tenses/have_to.htm
https://www.englisch-hilfen.de/en/exercises/modals/must_not.htm
https://www.englishexercises.org/makeagame/viewgame.asp?id=6812