https://www.ef.com.es/recursos-aprender-ingles/gramatica-inglesa/simple-past/
https://www.madridteacher.com/Grammar/pasado-simple.htm
https://english.lingolia.com/es/gramatica/tiempos-verbales/simple-past
https://agendaweb.org/verbs/past-simple.html
https://agendaweb.org/verbs/past_simple-exercises.html
https://www.esl-lounge.com/student/grammar/1g85-elementary-past-simple-multiple-choice-exercise.php
http://www.languageguide-online.com/past-simple---exercises.html