Forms 8a, 8c1, 8c2. Modals

For practicing:
https://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-87468.php;
http://www.focus.olsztyn.pl/en-modal-verbs-practice.html#.Xrkd0m5uLDd;
https://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-97711.php;
https://www.english-4u.de/en/grammar-exercises/modal-verbs.htm;
https://www.english-4u.de/en/grammar-exercises/modal-verbs2.htm;
https://www.english-4u.de/en/grammar-exercises/modal-verbs3.htm;
https://www.english-4u.de/en/grammar-exercises/modal-verbs4.htm;
https://www.english-4u.de/en/grammar-exercises/modal-verbs5.htm;
https://www.english-4u.de/en/grammar-exercises/modal-verbs6.htm.