Jenks, C. Wilfred
Stevens & Sons Limited, 1960
Buku Teks
Jenks, C. Wilfred
Oxford University Press, 1970
Buku Teks
Ferrell, Wilfred A
Holt, Rinehart and Winston, 1978
Buku Teks
Gordon, Scott
Columbia University Press, 1980
Buku Teks
Jenks, Edward
Murray, 1936
Buku Klasik