http://www.ego4u.com/en/cram-up/grammar/relative-clauses/exercises?02

http://www.ego4u.com/en/cram-up/tests/relative-clauses-1

http://www.montsemorales.com/gramatica/DefinRelatImag4-33.htm

http://esl.fis.edu/grammar/multi/relative1.htm

http://www.englishexercises.org/makeagame/viewgame.asp?id=1255