Merriam-Webster, 1985
Buku Referensi
Rosenberg, Jerry M., author
McGraw-Hill, 1992
Buku Referensi
Brown, Wendy E., author
McGraw-Hill, 1993
Buku Referensi
Wandelt, Ingo, author
Friedrich Ebert Stiftung (FES) Indonesia Office, 2009
Buku Referensi
editor, Jennifer Mossman
Gale Research, 1990
Buku Referensi