http://www.xtec.cat/~jgenover/catgra10.htm
http://www.spanish.cl/Grammar/Games/Interrogativos.htm
http://www.spanish.cl/Grammar/Games/Interrogativos_2.htm
http://www.languagesonline.org.uk/Spanish/Vocabulary/Questions/2.htm
http://www.123teachme.com/spanish_sentence_quiz/category/quien_quienes_1
https://espanol.lingolia.com/es/gramatica/pronombres-y-determinantes/pronombres-relativos/ejercicios
http://www.espagnolfacile.com/exercices/exercice-espagnol-2/exercice-espagnol-11940.php
http://mld.ursinus.edu/~jarana/Ejercicios/self-check/relative_pronouns1.html
http://www.espagnolfacile.com/exercices/exercice-espagnol-2/exercice-espagnol-20784.php