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English Plus+
English Plus: Grammar Slammar!
An easy-to-use grammar resource containing rules for style, usage, capitalization, abbreviations, punctuation, and letter writing. This site also includes a glossary of common grammatical mistakes.
University of Calgary
University of Calgary: Basic Elements of English
Sections include parts of speech, sentence elements, punctuation, and word use. Also includes a "brief explanations of common writing errors." The tutorials also include interactive quizzes to check your understanding.
English Club
English Club: Six Common Mistakes in Esl Writing
This EnglishClub tutorial provides a list, with brief explanations, of the most common writing mistakes made among English as a Second Language students.