Plaskitt, Harold, author
University Tujorial Press, 1950
Buku Teks
Grove, J.M.
Longmans, 1962
Buku Teks
Moodie, Graeme C., author
Crowell, 1971
Buku Teks
Lenin, Vladimir I., author
Foreign Languages Publishing House , [date of publication not identified]
Buku Teks
Brady, Robert A.
University of California Press, 1950
Buku Teks