http://www.englisch-hilfen.de/en/exercises/questions/simple_past.htm
http://www.englisch-hilfen.de/en/exercises/questions/simple_past2.htm
http://www.englisch-hilfen.de/en/exercises/tenses/simple_past_statements2.htm
http://www.englisch-hilfen.de/en/exercises/tenses/simple_past_negation_sentences3.htm
http://www.chompchomp.com/irregular01/irregular01.htm
http://www.chompchomp.com/irregular02/irregular02.htm
http://www.chompchomp.com/irregular03/irregular03.htm
http://www.chompchomp.com/irregular04/irregular04.htm
http://www.chompchomp.com/irregular05/irregular05.htm
http://www.chompchomp.com/irregular06/irregular06.htm