Powell, Fred Wilbur
Brookings Institution, 1939
Buku Teks
University of Queensland Press, 1980
Buku Teks
Brandt, Conrad, author
George Allen and Unwin, 1959
Buku Teks
edited with an introd. by E. Bradford Burns
Alfred A. Knopf, 1966
Buku Teks
edited, Nathan Reingold; edited, Ida H. Reingold
University of Chicago Press, 1981
Buku Referensi