MODAL VERBS

CAN / COULD / BE ABLE TO

http://www.flo-joe.co.uk/fce/students/strategy/openclze/modals.htm

http://www.engvid.com/expressing-ability-can-could-be-able-to/

http://blog.myhappyenglish.com/2013/01/one-point-english-lesson-using-could/

http://curso-gratis-ingles.euroresidentes.com/2006/06/can-y-be-able-to-en-ingls.html

http://www.bbc.co.uk/worldservice/learningenglish/grammar/learnit/learnitv196.shtml

http://www.englishclub.com/grammar/verbs-modals_can_quiz.htm

http://perso.wanadoo.es/autoenglish/gr.can.i.htm

http://esl.about.com/library/quiz/blgrquiz_canbeable.htm

MUST / HAVE TO / SHOULD OBLIGATION

http://www.englishgrammarsecrets.com/musthaveto/menu.php

http://www.englishexercises.org/makeagame/viewgame.asp?id=6958

http://www.englishgrammarsecrets.com/musthaveto/exercise7.html

http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-55666.php

http://www.englishpage.com/modals/interactivemodal2.htm

http://www.englishclub.com/grammar/verbs-modals-have-to-must-not-quiz.htm

http://english-zone.com/verbs/modals1.html

http://www.esl-classroom.com/grammar/shouldandmust1.html

http://www.autoenglish.org/modalverbs/ModalsObligation.htm