Past Simple Tense

http://www.daypo.com/verbos-irregulares-ingles-i.html

https://www.examtime.com/es/p/52879-ingl-s-selectividad---conjugaci-n-verbos-irregulares-flash_card_decks

http://aprendeinglessila.com/2013/01/como-memorizar-verbos-irregulares-parte-1/

http://mwl.epic.pearsoncmg.com/fileUpload/19002034/Verbos%20Irregulares%20y%20Regulares%20/VERBOS%20IRREGULARES1245853356359.pdf

http://aprenderbieninglesonline.blogspot.it/2014/04/verbos-irregulares-en-ingles-los-50.html