http://www.englishexercises.org/makeagame/viewgame.asp?id=10642
http://www.agendaweb.org/exercises/verbs/past-simple-regular
http://www.agendaweb.org/verbs/past-simple-regular/index.html
http://www.agendaweb.org/exercises/verbs/past-simple-regular-d-ed-ied.htm
http://www.adelescorner.org/grammar/past_tense/past_regular.html
http://www.kico4u.de/english/uebungen/unregelmaverb/regel1.htm
http://www.montsemorales.com/gramatica/PastSimRegPdc.htm
http://www.montsemorales.com/gramatica/PastSregular1y2.htm
http://www.montsemorales.com/gramatica/PastSimpAffRegSw2-4.htm
http://www.montsemorales.com/gramatica/PastRegPdcCr.htm