MARTIN, ANN THE BABY-SITTERS CLUB #21: MALLORY AND THE TROUBLE WITH TWINS - FIRST EDITION - NEW YORK SCHOLASTIC, INC. 1989 - 144P. - APPLE PAPERBACKS: THE BABY-SITTERS CLUB . BOOK NO. 21 IN SERIES ISBN: 0590420054 Subjects--Topical Terms: FICTION Dewey Class. No.: F/MAR/B