We will give a brief explanation of the PASSIVE VOICE
http://languagearts.pppst.com/active-passive-voice.html
And now it's time to practise. Come on !!
http://www.ego4u.com/en/cram-up/grammar/passive
http://www.ompersonal.com.ar/omexercise/vozpasiva/unit20.htm
http://www.englisch-hilfen.de/en/exercises_list/passiv.htm