Srewart, Desmond
New York : Time Incorporated, c.1962.
Buku Teks
edited by Waris Ishaq
Frederick A. Praeger, 1991
Buku Teks SO
Israel, Saul
Holt, Rinehart and Winston, 1976
Buku Teks SO
Federico, Ronald C.
McGraw-Hill, 1990
Buku Teks
edited by Don Hellriegel and John W. Slocum
Addison- Wesley , 1975
Buku Teks