https://agendaweb.org/exercises/verbs/past-continuous/write-1
https://www.englisch-hilfen.de/en/exercises/tenses/past_progressive_statements2.htm
http://www.focus.olsztyn.pl/en-exercises-past-continuous-test-1.html#.X9HitNgzZPY
https://www.montsemorales.com/gramatica/PastContinAffnegSw2-6.htm
https://www.english-grammar.at/online_exercises/tenses/t105-past-tense.htm
