F4 02.10 Grammar exercises

http://static.digischool.nl/en/grammar/hotpot/be/tegtijd.htm
http://www.web-esl.com/tobe/tobe20.htm
https://www.englisch-hilfen.de/en/exercises/tenses/be.htm
https://www.grammarbank.com/verb-to-be-exercise.html
http://elovivo.com/introenglish/en/intro_english/lessons_wordlist/basic_english_lesson_01/lesson01b_ex.html