http://www.usingenglish.com/quizzes/235.html
http://www.englishexercises.org/makeagame/viewgame.asp?id=1394
http://www.englishexercises.org/makeagame/viewgame.asp?id=4433
http://michel.barbot.pagesperso-orange.fr/hotpot/since_for/sincefor1.htm
http://www.adelescorner.org/grammar/for_since/for-since2.html
http://www.englishexercises.net/yyforsince.html
http://www.discip.crdp.ac-caen.fr/anglais/documents/america2/K.htm
http://www.impact-english.com/members/Grammar_Practice/Always/test-grammar/gr_prac_S-F-gen.htm
http://www.english-4u.de/for_since_ex1.htm
http://www.funteaching.it/project/engl2005/basic/forsince.htm