LINKS::::
http://www.englishexercises.org/makeagame/viewgame.asp?id=3826#a
http://www.esltower.com/GRAMMARQUIZ/modals/can,%20can't,%20couldn't,%20could%20-%20output/modal1.html
http://english-zone.com/verbs/can-cant.html
http://virginiasm-virginia.blogspot.com/2010/03/can-could-exercises.html