more PASSIVE forms practice!

There's been some difficulty with passive exercises in the unit tests recently, so here are a few links to revise this grammar structure:
http://www.englishgrammarsecrets.com/passive/exercise1.html
http://www.englishgrammarsecrets.com/passive/exercise2.html
http://www.englishgrammarsecrets.com/passive/exercise3.html
http://www.englishgrammarsecrets.com/passive/exercise4.html
http://www.englishgrammarsecrets.com/passive/exercise5.html
http://www.englishgrammarsecrets.com/passive/exercise6.html