ćwiczenia online:
http://www.anglomaniacy.pl/grammar-verbs-learn1.htm
http://www.englishmaven.org/HP6/To_Be_Exercise4.htm
http://www.myenglishpages.com/site_php_files/grammar-exercise-be-present.php#.VDpgD_l_uHQ
http://www.englishmaven.org/HP6/To_Be_Exercise6.htm
http://www.agendaweb.org/verbs/to-be-exercises.html