Past Tense

1. Betty Schrampfer Azar. (1989). Understanding and using English grammar. Prentice Hall Regents.

2. Betty Schrampfer Azar. (1996). Basic English grammar. Prentice Hall Regents.

3. Connelly, M. (2007). Get writing : Paragraphs and essays. Thomson Wadsworth.
4. Murphy, R. (2019). English grammar in use. Cambridge University Press.