Exercises to practise relative pronouns

http://www.esl-lounge.com/student/grammar/3g31-relative-clause-gap-fill-exercise.php

http://www.ihbristol.com/free-english-exercises/test/esol-smc-who-what-which-where

http://www.english-grammar.at/online_exercises/relative-pronouns/rp001-relative-pronouns.htm