Ehrmann, Henry W.
Prentice-Hall, 1976
Buku Teks
Glendon, Mary Ann
West Academic Publishing, 1999
Buku Teks
David, Rene, 1906-
Stevens & sons, 1985
Buku Teks
Katsh, M. Ethan
McGaraw-Hill, 1998
Buku Teks
Gutteridge, H. C.
Cambridge University Press, 1949
Buku Teks