http://www.myenglishpages.com/site_php_files/grammar-exercise-modals.php
http://www.perfect-english-grammar.com/modal-verbs-of-probability-exercise-2.html
http://www.perfect-english-grammar.com/modal-verbs-of-ability-exercise-1.html
http://www.learnenglish-online.com/grammar/modals/tests/modaltest2.html
http://www.english-4u.de/modal_verbs_ex2.htm