level 1 = https://www.englishspanishlink.com/en/english-grammar-exercises/passive-voice_2.htm (omzetten present and past simple)
level 2 = Omzetten: maak van de active zinnen een passive all tenses
https://www.ego4u.com/en/cram-up/grammar/passive/exercises?06
https://www.english-grammar.at/online_exercises/passive-voice/pa15.htm
https://www.english-grammar.at/online_exercises/passive-voice/pa006-active-passive.htm
level 3 = Omzetten met two objects (lijdend voorwerp en meewerken voorwerp):
https://www.englisch-hilfen.de/en/exercises/active_passive/objects_tenses.htm