Burger, W. V. (1935). Teacher's manual for Ditto directed study lessons in American history. Ditto, Inc..
Lua i Stíl Chicago (17ú heag.)Burger, William V. Teacher's Manual for Ditto Directed Study Lessons in American History. Chicago: Ditto, Inc., 1935.
Lua MLA (8ú heag.)Burger, William V. Teacher's Manual for Ditto Directed Study Lessons in American History. Ditto, Inc., 1935.
Rabhadh: Seans nach mbeach na luanna seo go hiomlán cruinn i ngach uile chás.