PASSIVE VOICE exercises

http://www.learnenglishfeelgood.com/esl-passive-voice-exercise2.html

http://www.myenglishpages.com/site_php_files/grammar-exercise-passive.php

http://www.englisch-hilfen.de/en/exercises/active_passive/passive_sentences1.htm

http://www.englisch-hilfen.de/en/exercises/active_passive/sentences_gaps.htm