Regan, William
Harper & Row, Publishers, 1970
Buku Teks
edited by Robert M. Hashway
Praeger, 1990
Buku Referensi
Bestor, Arthur
Knopf, 1956
Buku Teks
Grambs, Jean D.
Holt, Rinehart and Winston, 1964
Buku Teks
Stoff, Sheldon Ptaschevitch, author
Harper & Row , 1969
Buku Teks