Brubaker, Sterling
A Mentor Book, 1972
Buku Teks
Bennett, Charles F.
John Wiley & Sons, 1975
Buku Teks
Knapp, B.J.
George Allen and Unwin, 1982
Buku Teks
Watson, Richard A.
Harcourt, Brace and World, 1969
Buku Teks
Voice of American Forum Lectures, 1968
Buku Teks