SINCE-FOR

http://www.englisch-hilfen.de/en/exercises/confusing_words/since_for.htm
http://www.englisch-hilfen.de/en/exercises/confusing_words/since_for2.htm
http://www.englishexercises.org/makeagame/viewgame.asp?id=1394
http://www.englishexercises.net/yyforsince.html
http://www.focus.olsztyn.pl/en-present-perfect-since-for-exercises.html#.WDdaGObhDIU
http://perso.ya.com/mjandres/archivos/since&for.htm