A friend who teaches and tutors ESL recommends the resources on this site.
https://www.learnenglishfeelgood.com/
Thank you, AlpheccaStars, for your recommendation. Others had recommended the same site to me, too. I have a few more recommended sites:
- http://www.grammar-quizzes.com
- https://www.englisch-hilfen.de/en
- http://www.eslcafe.com
- https://www.englishgrammarsecrets.com
- https://www.englishpage.com
- https://www.grammarbank.com
- https://www.perfect-english-grammar.com/
- https://web2.uvcs.uvic.ca/elc/studyzone/grammar.htm
- https://www.ego4u.com/
- http://perso.wanadoo.es/autoenglish/freeexercises.htm
https://www.learnenglishfeelgood.com/