Peacock, James
Prentice-Hall, 1980
Buku Teks
Boulding, Kenneth E. (Kenneth Ewart), 1910-1993, author
Beverly Hull, 1985
Buku Teks
[publisher not identified], [date of publication no identified]
Buku Teks
Davis, Kingsley, 1908-1997, author
Macmillan, 1964
Buku Teks
Firth, Raymond, author
Thomas Nelson and Sons, 1947
Buku Teks