Passive voice

Hello all, here are a few links to explanation and exercises on passive voice.
check them out.
enjoy
http://www.ego4u.com/en/cram-up/grammar/passive

http://www.aprenderinglesfacil.es/2009/01/passive-voice-voz-pasiva.html

http://www.englisch-hilfen.de/en/exercises_list/passiv.htm