Relative clauses

Explanations:
 http://www.perfect-english-grammar.com/relative-clauses.html
 http://www.ego4u.com/en/cram-up/grammar/relative-clauses

Exercises:
http://www.englischhilfen.de/en/exercises/pronouns/relative_pronouns.htm http://www.englishexercises.org/makeagame/viewgame.asp?id=6084
http://www.englishexercises.org/exercise.asp?id=7732