Williams, Robert I., editor
Prentice-Hall, 1956
Buku Referensi
Carlson, Arthur E., author
South-Western Publishing , 1982
Buku Teks
Brock, Horace R., author
McGraw-Hill, 1986
Buku Teks
Skousen, K. Fred, author
Salembe Empat, 2001
Buku Teks
Welsch, Glenn A., author
Learning System Company, 1977
Buku Teks