Suggestions for materials. Go to:
Advanced students
http://www.testden.com/challenge/free-toefl-gsa.asp (this is for you Onima)
Current students
http://www.usingenglish.com/quizzes/37.html (Verb to Be)
http://www.englishclub.com/grammar/verb-tenses_present-continuous_quiz.htm (Present Progressive)
http://www.usingenglish.com/quizzes/65.html (Present Simple)
