Meriam, James L., author
John Wiley & Sons, 1975
Buku Teks
Sheriff, Robert E., author
Cambridge University Press, 1994
Buku Teks
Buku Teks
Hale, John R., author
Time-Life Books, 1974
Buku Teks
Abell, George O., author
Holt Rinehart and Winston, 1974
Buku Teks