past simple vs past continuous http://www.bbc.co.uk/learningenglish/english/course/lower-intermediate/unit-7/session-2
past perfect simple or continuous? https://elt.oup.com/student/solutions/upperint/grammar/grammar_02_022e?cc=hu&selLanguage=hu
past simple or past perfect? http://www.tolearnenglish.com/exercises/exercise-english-2/exercise-english-54353.php
irregular V3 http://www.englisch-hilfen.de/en/exercises/irregular_verbs/crossword_past_participle.htm
past simple vs. past continuous http://www.englisch-hilfen.de/en/exercises/tenses/simple_past_progressive.htm