exercises verb TO BE

http://www.englisch-hilfen.de/en/exercises/questions/be.htm
http://www.englisch-hilfen.de/en/exercises/tenses/be3.htm
http://www.myenglishpages.com/site_php_files/grammar-exercise-be-present.php
http://www.learnenglishfeelgood.com/english-verbs-tobe1.html
http://www.englishbee.net/lessons/basic_exer/tobe/tobe_quiz1/to_be_quiz_1.htm