noun

plural noun: auxiliary verbs

1. a verb used in forming the tenses, moods, and voices of other verbs. The primary auxiliary verbs in English are be, do, and have ; the modal auxiliaries are can, could, may, might, must, shall, should, will, and would.

   http://grammar.ccc.commnet.edu/grammar/auxiliary.htm

   Online tests:

   https://www.ecenglish.com/learnenglish/lessons/be-do-and-have-auxiliary-verbs

   https://www.thoughtco.com/auxiliary-helping-verb-use-quiz-4071877

   https://www.usingenglish.com/quizzes/42.html

   https://www.learnenglishfeelgood.com/english-auxiliary-verbs1.html

   https://www.proprofs.com/quiz-school/story.php?title=auxiliary-verbs

   https://www.myenglishpages.com/site_php_files/grammar-exercise-auxiliary-verbs.php

   https://agendaweb.org/verbs/be_can_do_have-exercises.html