1. https://www.englisch-hilfen.de/en/complex_tests/passive1/index.php
2. https://www.englisch-hilfen.de/en/exercises/active_passive/active_or_passive.htm
3. https://www.englisch-hilfen.de/en/exercises/active_passive/questions.htm
4. https://www.english-grammar.at/online_exercises/passive-voice/pa014.htm
5. https://www.english-grammar.at/online_exercises/passive-voice/pa013-passive-active.htm
6. https://www.english-grammar.at/online_exercises/passive-voice/pa003-history-of-paper.htm
7. https://multimedia-english.com/activities/free/passive-voice-737
8. https://agendaweb.org/exercises/verbs/passive-1
9. http://static.digischool.nl/en/grammar/hotpot/passive/tegenverltijd.htm
10. http://www.eslgamesplus.com/passive-voice-past-passive-esl-grammar-sentence-activity-fun-game-online/
11. https://www.englishmedialab.com/GrammarGames/football/passive%20voice/passive%20voice.html
12. http://www.eslgamesworld.com/members/games/grammar/basketball/active%20vs.%20passive%20voice/active%20vs.%20passive%20voice.html
13. https://www.turacogames.com/games/passive-voice-grammar-game-for-esl/
14. https://www.mes-games.com/passive1.php