Westring, Gosta B.
N.Y. United Nations Institute for traning and research , 1974
Buku Teks
Saye, Albert B.
Prentice-Hall, 1966
Buku Teks
English, Jack
McGraw-Hill, 1992
Buku Teks
edited by George A. Hawkins
McGraw-Hill, 1968
Buku Teks
cordinating editor, Geoge A. Hawkins
McGraw-Hill, 1968
Buku Teks