Tabela de verbos Irregulares
http://www.ego4u.com/en/cram-up/grammar/present-perfect-simple/exercises?06
http://www2.gsu.edu/~wwwesl/egw/verbs.htm
http://www.english-zone.com/verbs/verbchrt.html
Exercícios de fixação http://www.englisch-hilfen.de/en/exercises_list/verbs.htm
