Godson, Roy
Macmillan, 1978
Buku Teks
edited by Rudolf L. Tokes
New York University Press, 1978
Buku Teks
Leonhard, Wolfgang
Rinehart and Winston, 1978
Buku Teks
Skilling, Gordon H., author
Thomas Y. Crowell, 1966
Buku Teks
Seton-Watson, Hugh, author
Methuen , 1950
Buku Teks