Azar, Betty Schrampfer Understanding and using English grammar : answer key / Betty Schrampfer Azar - 3rd ed. - New York. : Longman/Prentice Hall Regents, 1999 - 108 p. ISBN: 0130205524 Subjects--Index Terms: Ngôn ngữ Ngữ pháp Tiếng Anh Dewey Class. No.: 428.2