Johnson, Richard E.
Reading, Mass. Addison-Wesley c.1962,
Buku Teks
Hall, James E., author
Brooks/Cole, 1971
Buku Teks
Zelinsky, Daniel, author
Academic Press, 1968
Buku Teks
Buchanan, Herbert E., author
Houghton Mifflin, 1928
Buku Teks
Leffler, John E.
Macmillan, 1973
Buku Teks