The Open University. Course Team
The Open University Press, 1984
Buku Referensi
Yasso, Warren E.
New York: Holt, Rinehart and Winston, 1965
Buku Teks
Yasso, Warren E.
New York: Holt, Rinehart and Winston, 1965
Buku Teks
Williams, Joreme
Little, Brown And Company, 1962
Buku Teks
Davis, Richard A.
Wm.C. Brown Publishers, 1996
Buku Teks