(1989). Understanding and using English grammer/Betty Schrampfer Azar (Edisi dwibahasa inggris-indonesia 2nd.ed). [S l. :: Prentice hall regents.
"Understanding and using English grammer/Betty Schrampfer Azar". Edisi dwibahasa inggris-indonesia 2nd.ed [S l. :: Prentice hall regents, 1989. .