useful websites to study passive voice

http://www.ego4u.com/en/cram-up/grammar/passive#exercises

http://web2.uvcs.uvic.ca/elc/studyzone/410/reading/exercises/dogqz.htm

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

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

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

http://www.englisch-hilfen.de/en/grammar_list/passiv.htm (IF YOU NEED SOME MORE EXPLANATION ON HOW TO FORM PASSIVE)

http://esl.about.com/library/quiz/blgrquiz_passive1.htm

http://www.eslgo.com/quizzes/raiderspassive.html


http://www.better-english.com/grammar/passive1.htm

http://a4esl.org/q/h/vm/active-passive.html