This website offers very concise explanation of the passive voice.
http://www.npc.edu.hk/staff/~ngtungying/english_grammar/lessons/lesson35.htm
Archive for the ‘English Grammar’ Category
被動語態 Passive Voice
Wednesday, April 30th, 2008主詞與動詞的ㄧ致–表格篇 Agreement between the subject and the verb
Tuesday, April 29th, 2008Please click 主詞與動詞的一致.doc
Agreement between the subject and the verb 主詞與動詞的一致
Monday, April 28th, 2008You might like to get some idea from this website:
http://blog.sina.com.tw/suchin/article.php?pbgid=18254&entryid=3195