http://www.englisch-hilfen.de/en/exercises/questions/question_tags3.htm
http://www.ego4u.de/de/cram-up/grammar/question-tags/exercises
http://www.englishgrammarsecrets.com/questionstags/exercise1.html
http://www.ego4u.com/en/cram-up/grammar/question-tags/exercises
http://www.englishgrammarsecrets.com/questionstags/exercise2.html
http://www.englishgrammarsecrets.com/questionstags/exercise4.html
http://www.englishgrammarsecrets.com/questionstags/exercise5.html
http://www.esl-lounge.com/student/grammar/2g16-question-tags-exercise.php
