Kirgis, Frederic L.
West Publishing, 1993
Buku Teks SO
Okolie, Charles Chukwuma
Frederick A. Praeger, 1975
Buku Teks
edited by Julio Faundez
St. Martin`s Press, 1997
Buku Teks SO
Benham, Frederic
Oxford University Press, 1962
Buku Teks
edited by Evan Luard
Praeger, 1966
Buku Teks SO