Morgan, James C.
The Free Press, 1991
Buku Teks
Alexander, Ralph
Richard D. Irwin , 1961
Buku Teks
Keegan, Warren J., author
Pearson, 2011
Buku Teks
Narver, John C., author
Holt, Rinehart and Winston, 1971
Buku Teks
Keegan, Warren J., author
Prenhallindo, 1996
Buku Teks