MODALS. UNIT 4

Here you can pracise a lot:

http://www.agendaweb.org/verbs/modals-exercises.html

http://www.xtec.cat/~ogodoy/sac/rephrasing/rephrexercises.htm

http://www.englishpage.com/modals/interactivemodal1.htm

http://www.perfect-english-grammar.com/modal-verbs-exercises.html