http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-18159.php

 

http://esl.fis.edu/grammar/multi/modal1.htm

http://www.english-grammar-lessons.com/should/exercise5.swf

http://www.ihbristol.com/free-english-exercises/test/esol-smc-modal-verbs