http://www.oup.com/elt/global/products/livinggrammar/int/b_exercises/ba_questions/2_1/
http://www.englishpage.com/modals/interactivemodal1.htm
http://www.englishpage.com/modals/interactivemodal2.htm
http://www.englishpage.com/modals/interactivemodal3.htm
http://www.englishpage.com/modals/interactivemodal7.htm
http://www.autoenglish.org/modalverbs.htm ( CHOOSE THE ONLINE OPTION)
http://www.nonstopenglish.com/lang/es/exercise.asp?exid=914
http://www.nonstopenglish.com/lang/es/exercise.asp?exid=917
http://www.englishexercises.org/makeagame/viewgame.asp?id=3738
http://www.englishexercises.org/makeagame/viewgame.asp?id=1793#a
http://www.englishexercises.org/makeagame/viewgame.asp?id=3023